Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3323 insertions, 0 deletions

diff --git a/layout/base/nsRefreshDriver.cpp b/layout/base/nsRefreshDriver.cpp
new file mode 100644
index 0000000000..af780bb192
--- /dev/null
+++ b/layout/base/nsRefreshDriver.cpp
@@ -0,0 +1,3323 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Code to notify things that animate before a refresh, at an appropriate
+ * refresh rate.  (Perhaps temporary, until replaced by compositor.)
+ *
+ * Chrome and each tab have their own RefreshDriver, which in turn
+ * hooks into one of a few global timer based on RefreshDriverTimer,
+ * defined below.  There are two main global timers -- one for active
+ * animations, and one for inactive ones.  These are implemented as
+ * subclasses of RefreshDriverTimer; see below for a description of
+ * their implementations.  In the future, additional timer types may
+ * implement things like blocking on vsync.
+ */
+
+#include "nsRefreshDriver.h"
+#include "mozilla/DataMutex.h"
+#include "nsThreadUtils.h"
+
+#ifdef XP_WIN
+#  include <windows.h>
+// mmsystem isn't part of WIN32_LEAN_AND_MEAN, so we have
+// to manually include it
+#  include <mmsystem.h>
+#  include "WinUtils.h"
+#endif
+
+#include "mozilla/AnimationEventDispatcher.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/dom/MediaQueryList.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/DisplayPortUtils.h"
+#include "mozilla/Hal.h"
+#include "mozilla/InputTaskManager.h"
+#include "mozilla/IntegerRange.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/VsyncTaskManager.h"
+#include "nsITimer.h"
+#include "nsLayoutUtils.h"
+#include "nsPresContext.h"
+#include "imgRequest.h"
+#include "nsComponentManagerUtils.h"
+#include "mozilla/Logging.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/DocumentInlines.h"
+#include "nsIXULRuntime.h"
+#include "jsapi.h"
+#include "nsContentUtils.h"
+#include "nsTextFrame.h"
+#include "mozilla/PendingFullscreenEvent.h"
+#include "mozilla/dom/PerformanceMainThread.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/StaticPrefs_apz.h"
+#include "mozilla/StaticPrefs_gfx.h"
+#include "mozilla/StaticPrefs_idle_period.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/StaticPrefs_page_load.h"
+#include "nsViewManager.h"
+#include "GeckoProfiler.h"
+#include "mozilla/dom/BrowserChild.h"
+#include "mozilla/dom/CallbackDebuggerNotification.h"
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/dom/Event.h"
+#include "mozilla/dom/Performance.h"
+#include "mozilla/dom/Selection.h"
+#include "mozilla/dom/VsyncMainChild.h"
+#include "mozilla/dom/WindowBinding.h"
+#include "mozilla/dom/LargestContentfulPaint.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
+#include "mozilla/RestyleManager.h"
+#include "mozilla/TaskController.h"
+#include "imgIContainer.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "nsDocShell.h"
+#include "nsISimpleEnumerator.h"
+#include "nsJSEnvironment.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/Telemetry.h"
+
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "VsyncSource.h"
+#include "mozilla/VsyncDispatcher.h"
+#include "mozilla/Unused.h"
+#include "nsAnimationManager.h"
+#include "nsDisplayList.h"
+#include "nsDOMNavigationTiming.h"
+#include "nsTransitionManager.h"
+
+#if defined(MOZ_WIDGET_ANDROID)
+#  include "VRManagerChild.h"
+#endif  // defined(MOZ_WIDGET_ANDROID)
+
+#include "nsXULPopupManager.h"
+
+#include <numeric>
+
+using namespace mozilla;
+using namespace mozilla::widget;
+using namespace mozilla::ipc;
+using namespace mozilla::dom;
+using namespace mozilla::layout;
+
+static mozilla::LazyLogModule sRefreshDriverLog("nsRefreshDriver");
+#define LOG(...) \
+  MOZ_LOG(sRefreshDriverLog, mozilla::LogLevel::Debug, (__VA_ARGS__))
+
+// after 10 minutes, stop firing off inactive timers
+#define DEFAULT_INACTIVE_TIMER_DISABLE_SECONDS 600
+
+// The number of seconds spent skipping frames because we are waiting for the
+// compositor before logging.
+#if defined(MOZ_ASAN)
+#  define REFRESH_WAIT_WARNING 5
+#elif defined(DEBUG) && !defined(MOZ_VALGRIND)
+#  define REFRESH_WAIT_WARNING 5
+#elif defined(DEBUG) && defined(MOZ_VALGRIND)
+#  define REFRESH_WAIT_WARNING (RUNNING_ON_VALGRIND ? 20 : 5)
+#elif defined(MOZ_VALGRIND)
+#  define REFRESH_WAIT_WARNING (RUNNING_ON_VALGRIND ? 10 : 1)
+#else
+#  define REFRESH_WAIT_WARNING 1
+#endif
+
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(nsRefreshDriver::TickReasons);
+
+namespace {
+// The number outstanding nsRefreshDrivers (that have been created but not
+// disconnected). When this reaches zero we will call
+// nsRefreshDriver::Shutdown.
+static uint32_t sRefreshDriverCount = 0;
+}  // namespace
+
+namespace mozilla {
+
+static TimeStamp sMostRecentHighRateVsync;
+
+static TimeDuration sMostRecentHighRate;
+
+/*
+ * The base class for all global refresh driver timers.  It takes care
+ * of managing the list of refresh drivers attached to them and
+ * provides interfaces for querying/setting the rate and actually
+ * running a timer 'Tick'.  Subclasses must implement StartTimer(),
+ * StopTimer(), and ScheduleNextTick() -- the first two just
+ * start/stop whatever timer mechanism is in use, and ScheduleNextTick
+ * is called at the start of the Tick() implementation to set a time
+ * for the next tick.
+ */
+class RefreshDriverTimer {
+ public:
+  RefreshDriverTimer() = default;
+
+  NS_INLINE_DECL_REFCOUNTING(RefreshDriverTimer)
+
+  virtual void AddRefreshDriver(nsRefreshDriver* aDriver) {
+    LOG("[%p] AddRefreshDriver %p", this, aDriver);
+
+    bool startTimer =
+        mContentRefreshDrivers.IsEmpty() && mRootRefreshDrivers.IsEmpty();
+    if (IsRootRefreshDriver(aDriver)) {
+      NS_ASSERTION(!mRootRefreshDrivers.Contains(aDriver),
+                   "Adding a duplicate root refresh driver!");
+      mRootRefreshDrivers.AppendElement(aDriver);
+    } else {
+      NS_ASSERTION(!mContentRefreshDrivers.Contains(aDriver),
+                   "Adding a duplicate content refresh driver!");
+      mContentRefreshDrivers.AppendElement(aDriver);
+    }
+
+    if (startTimer) {
+      StartTimer();
+    }
+  }
+
+  void RemoveRefreshDriver(nsRefreshDriver* aDriver) {
+    LOG("[%p] RemoveRefreshDriver %p", this, aDriver);
+
+    if (IsRootRefreshDriver(aDriver)) {
+      NS_ASSERTION(mRootRefreshDrivers.Contains(aDriver),
+                   "RemoveRefreshDriver for a refresh driver that's not in the "
+                   "root refresh list!");
+      mRootRefreshDrivers.RemoveElement(aDriver);
+    } else {
+      nsPresContext* pc = aDriver->GetPresContext();
+      nsPresContext* rootContext = pc ? pc->GetRootPresContext() : nullptr;
+      // During PresContext shutdown, we can't accurately detect
+      // if a root refresh driver exists or not. Therefore, we have to
+      // search and find out which list this driver exists in.
+      if (!rootContext) {
+        if (mRootRefreshDrivers.Contains(aDriver)) {
+          mRootRefreshDrivers.RemoveElement(aDriver);
+        } else {
+          NS_ASSERTION(mContentRefreshDrivers.Contains(aDriver),
+                       "RemoveRefreshDriver without a display root for a "
+                       "driver that is not in the content refresh list");
+          mContentRefreshDrivers.RemoveElement(aDriver);
+        }
+      } else {
+        NS_ASSERTION(mContentRefreshDrivers.Contains(aDriver),
+                     "RemoveRefreshDriver for a driver that is not in the "
+                     "content refresh list");
+        mContentRefreshDrivers.RemoveElement(aDriver);
+      }
+    }
+
+    bool stopTimer =
+        mContentRefreshDrivers.IsEmpty() && mRootRefreshDrivers.IsEmpty();
+    if (stopTimer) {
+      StopTimer();
+    }
+  }
+
+  TimeStamp MostRecentRefresh() const { return mLastFireTime; }
+  VsyncId MostRecentRefreshVsyncId() const { return mLastFireId; }
+  virtual bool IsBlocked() { return false; }
+
+  virtual TimeDuration GetTimerRate() = 0;
+
+  TimeStamp GetIdleDeadlineHint(TimeStamp aDefault) {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    if (!IsTicking() && !gfxPlatform::IsInLayoutAsapMode()) {
+      return aDefault;
+    }
+
+    TimeStamp mostRecentRefresh = MostRecentRefresh();
+    TimeDuration refreshPeriod = GetTimerRate();
+    TimeStamp idleEnd = mostRecentRefresh + refreshPeriod;
+    double highRateMultiplier = nsRefreshDriver::HighRateMultiplier();
+
+    // If we haven't painted for some time, then guess that we won't paint
+    // again for a while, so the refresh driver is not a good way to predict
+    // idle time.
+    if (highRateMultiplier == 1.0 &&
+        (idleEnd +
+             refreshPeriod *
+                 StaticPrefs::layout_idle_period_required_quiescent_frames() <
+         TimeStamp::Now())) {
+      return aDefault;
+    }
+
+    // End the predicted idle time a little early, the amount controlled by a
+    // pref, to prevent overrunning the idle time and delaying a frame.
+    // But do that only if we aren't in high rate mode.
+    idleEnd = idleEnd - TimeDuration::FromMilliseconds(
+                            highRateMultiplier *
+                            StaticPrefs::layout_idle_period_time_limit());
+    return idleEnd < aDefault ? idleEnd : aDefault;
+  }
+
+  Maybe<TimeStamp> GetNextTickHint() {
+    MOZ_ASSERT(NS_IsMainThread());
+    TimeStamp nextTick = MostRecentRefresh() + GetTimerRate();
+    return nextTick < TimeStamp::Now() ? Nothing() : Some(nextTick);
+  }
+
+  // Returns null if the RefreshDriverTimer is attached to several
+  // RefreshDrivers. That may happen for example when there are
+  // several windows open.
+  nsPresContext* GetPresContextForOnlyRefreshDriver() {
+    if (mRootRefreshDrivers.Length() == 1 && mContentRefreshDrivers.IsEmpty()) {
+      return mRootRefreshDrivers[0]->GetPresContext();
+    }
+    if (mContentRefreshDrivers.Length() == 1 && mRootRefreshDrivers.IsEmpty()) {
+      return mContentRefreshDrivers[0]->GetPresContext();
+    }
+    return nullptr;
+  }
+
+  bool IsAnyToplevelContentPageLoading() {
+    for (nsTArray<RefPtr<nsRefreshDriver>>* drivers :
+         {&mRootRefreshDrivers, &mContentRefreshDrivers}) {
+      for (RefPtr<nsRefreshDriver>& driver : *drivers) {
+        if (nsPresContext* pc = driver->GetPresContext()) {
+          if (pc->Document()->IsTopLevelContentDocument() &&
+              pc->Document()->GetReadyStateEnum() <
+                  Document::READYSTATE_COMPLETE) {
+            return true;
+          }
+        }
+      }
+    }
+
+    return false;
+  }
+
+ protected:
+  virtual ~RefreshDriverTimer() {
+    MOZ_ASSERT(
+        mContentRefreshDrivers.Length() == 0,
+        "Should have removed all content refresh drivers from here by now!");
+    MOZ_ASSERT(
+        mRootRefreshDrivers.Length() == 0,
+        "Should have removed all root refresh drivers from here by now!");
+  }
+
+  virtual void StartTimer() = 0;
+  virtual void StopTimer() = 0;
+  virtual void ScheduleNextTick(TimeStamp aNowTime) = 0;
+
+ public:
+  virtual bool IsTicking() const = 0;
+
+ protected:
+  bool IsRootRefreshDriver(nsRefreshDriver* aDriver) {
+    nsPresContext* pc = aDriver->GetPresContext();
+    nsPresContext* rootContext = pc ? pc->GetRootPresContext() : nullptr;
+    if (!rootContext) {
+      return false;
+    }
+
+    return aDriver == rootContext->RefreshDriver();
+  }
+
+  /*
+   * Actually runs a tick, poking all the attached RefreshDrivers.
+   * Grabs the "now" time via TimeStamp::Now().
+   */
+  void Tick() {
+    TimeStamp now = TimeStamp::Now();
+    Tick(VsyncId(), now);
+  }
+
+  void TickRefreshDrivers(VsyncId aId, TimeStamp aNow,
+                          nsTArray<RefPtr<nsRefreshDriver>>& aDrivers) {
+    if (aDrivers.IsEmpty()) {
+      return;
+    }
+
+    for (nsRefreshDriver* driver : aDrivers.Clone()) {
+      // don't poke this driver if it's in test mode
+      if (driver->IsTestControllingRefreshesEnabled()) {
+        continue;
+      }
+
+      TickDriver(driver, aId, aNow);
+    }
+  }
+
+  /*
+   * Tick the refresh drivers based on the given timestamp.
+   */
+  void Tick(VsyncId aId, TimeStamp now) {
+    ScheduleNextTick(now);
+
+    mLastFireTime = now;
+    mLastFireId = aId;
+
+    LOG("[%p] ticking drivers...", this);
+
+    TickRefreshDrivers(aId, now, mContentRefreshDrivers);
+    TickRefreshDrivers(aId, now, mRootRefreshDrivers);
+
+    LOG("[%p] done.", this);
+  }
+
+  static void TickDriver(nsRefreshDriver* driver, VsyncId aId, TimeStamp now) {
+    driver->Tick(aId, now);
+  }
+
+  TimeStamp mLastFireTime;
+  VsyncId mLastFireId;
+  TimeStamp mTargetTime;
+
+  nsTArray<RefPtr<nsRefreshDriver>> mContentRefreshDrivers;
+  nsTArray<RefPtr<nsRefreshDriver>> mRootRefreshDrivers;
+
+  // useful callback for nsITimer-based derived classes, here
+  // because of c++ protected shenanigans
+  static void TimerTick(nsITimer* aTimer, void* aClosure) {
+    RefPtr<RefreshDriverTimer> timer =
+        static_cast<RefreshDriverTimer*>(aClosure);
+    timer->Tick();
+  }
+};
+
+/*
+ * A RefreshDriverTimer that uses a nsITimer as the underlying timer.  Note that
+ * this is a ONE_SHOT timer, not a repeating one!  Subclasses are expected to
+ * implement ScheduleNextTick and intelligently calculate the next time to tick,
+ * and to reset mTimer.  Using a repeating nsITimer gets us into a lot of pain
+ * with its attempt at intelligent slack removal and such, so we don't do it.
+ */
+class SimpleTimerBasedRefreshDriverTimer : public RefreshDriverTimer {
+ public:
+  /*
+   * aRate -- the delay, in milliseconds, requested between timer firings
+   */
+  explicit SimpleTimerBasedRefreshDriverTimer(double aRate) {
+    SetRate(aRate);
+    mTimer = NS_NewTimer();
+  }
+
+  virtual ~SimpleTimerBasedRefreshDriverTimer() override { StopTimer(); }
+
+  // will take effect at next timer tick
+  virtual void SetRate(double aNewRate) {
+    mRateMilliseconds = aNewRate;
+    mRateDuration = TimeDuration::FromMilliseconds(mRateMilliseconds);
+  }
+
+  double GetRate() const { return mRateMilliseconds; }
+
+  TimeDuration GetTimerRate() override { return mRateDuration; }
+
+ protected:
+  void StartTimer() override {
+    // pretend we just fired, and we schedule the next tick normally
+    mLastFireTime = TimeStamp::Now();
+    mLastFireId = VsyncId();
+
+    mTargetTime = mLastFireTime + mRateDuration;
+
+    uint32_t delay = static_cast<uint32_t>(mRateMilliseconds);
+    mTimer->InitWithNamedFuncCallback(
+        TimerTick, this, delay, nsITimer::TYPE_ONE_SHOT,
+        "SimpleTimerBasedRefreshDriverTimer::StartTimer");
+  }
+
+  void StopTimer() override { mTimer->Cancel(); }
+
+  double mRateMilliseconds;
+  TimeDuration mRateDuration;
+  RefPtr<nsITimer> mTimer;
+};
+
+/*
+ * A refresh driver that listens to vsync events and ticks the refresh driver
+ * on vsync intervals. We throttle the refresh driver if we get too many
+ * vsync events and wait to catch up again.
+ */
+class VsyncRefreshDriverTimer : public RefreshDriverTimer {
+ public:
+  // This is used in the parent process for all platforms except Linux Wayland.
+  static RefPtr<VsyncRefreshDriverTimer>
+  CreateForParentProcessWithGlobalVsync() {
+    MOZ_RELEASE_ASSERT(XRE_IsParentProcess());
+    MOZ_RELEASE_ASSERT(NS_IsMainThread());
+    RefPtr<VsyncDispatcher> vsyncDispatcher =
+        gfxPlatform::GetPlatform()->GetGlobalVsyncDispatcher();
+    RefPtr<VsyncRefreshDriverTimer> timer =
+        new VsyncRefreshDriverTimer(std::move(vsyncDispatcher), nullptr);
+    return timer.forget();
+  }
+
+  // This is used in the parent process for Linux Wayland only, where we have a
+  // per-widget VsyncSource which is independent from the gfxPlatform's global
+  // VsyncSource.
+  static RefPtr<VsyncRefreshDriverTimer>
+  CreateForParentProcessWithLocalVsyncDispatcher(
+      RefPtr<VsyncDispatcher>&& aVsyncDispatcher) {
+    MOZ_RELEASE_ASSERT(XRE_IsParentProcess());
+    MOZ_RELEASE_ASSERT(NS_IsMainThread());
+    RefPtr<VsyncRefreshDriverTimer> timer =
+        new VsyncRefreshDriverTimer(std::move(aVsyncDispatcher), nullptr);
+    return timer.forget();
+  }
+
+  // This is used in the content process.
+  static RefPtr<VsyncRefreshDriverTimer> CreateForContentProcess(
+      RefPtr<VsyncMainChild>&& aVsyncChild) {
+    MOZ_RELEASE_ASSERT(XRE_IsContentProcess());
+    MOZ_RELEASE_ASSERT(NS_IsMainThread());
+    RefPtr<VsyncRefreshDriverTimer> timer =
+        new VsyncRefreshDriverTimer(nullptr, std::move(aVsyncChild));
+    return timer.forget();
+  }
+
+  TimeDuration GetTimerRate() override {
+    if (mVsyncDispatcher) {
+      mVsyncRate = mVsyncDispatcher->GetVsyncRate();
+    } else if (mVsyncChild) {
+      mVsyncRate = mVsyncChild->GetVsyncRate();
+    }
+
+    // If hardware queries fail / are unsupported, we have to just guess.
+    return mVsyncRate != TimeDuration::Forever()
+               ? mVsyncRate
+               : TimeDuration::FromMilliseconds(1000.0 / 60.0);
+  }
+
+  bool IsBlocked() override {
+    return !mSuspendVsyncPriorityTicksUntil.IsNull() &&
+           mSuspendVsyncPriorityTicksUntil > TimeStamp::Now() &&
+           ShouldGiveNonVsyncTasksMoreTime();
+  }
+
+ private:
+  // RefreshDriverVsyncObserver redirects vsync notifications to the main thread
+  // and calls VsyncRefreshDriverTimer::NotifyVsyncOnMainThread on it. It also
+  // acts as a weak reference to the refresh driver timer, dropping its
+  // reference when RefreshDriverVsyncObserver::Shutdown is called from the
+  // timer's destructor.
+  //
+  // RefreshDriverVsyncObserver::NotifyVsync is called from different places
+  // depending on the process type.
+  //
+  // Parent process:
+  // NotifyVsync is called by RefreshDriverVsyncDispatcher, on a background
+  // thread. RefreshDriverVsyncDispatcher keeps strong references to its
+  // VsyncObservers, both in its array of observers and while calling
+  // NotifyVsync. So it might drop its last reference to the observer on a
+  // background thread. This means that the VsyncRefreshDriverTimer itself can't
+  // be the observer (because its destructor would potentially be run on a
+  // background thread), and it's why we use this separate class.
+  //
+  // Child process:
+  // NotifyVsync is called by VsyncMainChild, on the main thread.
+  // VsyncMainChild keeps raw pointers to its observers.
+  class RefreshDriverVsyncObserver final : public VsyncObserver {
+    NS_INLINE_DECL_THREADSAFE_REFCOUNTING(
+        VsyncRefreshDriverTimer::RefreshDriverVsyncObserver, override)
+
+   public:
+    explicit RefreshDriverVsyncObserver(
+        VsyncRefreshDriverTimer* aVsyncRefreshDriverTimer)
+        : mVsyncRefreshDriverTimer(aVsyncRefreshDriverTimer),
+          mLastPendingVsyncNotification(
+              "RefreshDriverVsyncObserver::mLastPendingVsyncNotification") {
+      MOZ_ASSERT(NS_IsMainThread());
+    }
+
+    void NotifyVsync(const VsyncEvent& aVsync) override {
+      // Compress vsync notifications such that only 1 may run at a time
+      // This is so that we don't flood the refresh driver with vsync messages
+      // if the main thread is blocked for long periods of time
+      {  // scope lock
+        auto pendingVsync = mLastPendingVsyncNotification.Lock();
+        bool hadPendingVsync = pendingVsync->isSome();
+        *pendingVsync = Some(aVsync);
+        if (hadPendingVsync) {
+          return;
+        }
+      }
+
+      if (XRE_IsContentProcess()) {
+        // In the content process, NotifyVsync is called by VsyncMainChild on
+        // the main thread. No need to use a runnable, just call
+        // NotifyVsyncTimerOnMainThread() directly.
+        NotifyVsyncTimerOnMainThread();
+        return;
+      }
+
+      // In the parent process, NotifyVsync is called on the vsync thread, which
+      // on most platforms is different from the main thread, so we need to
+      // dispatch a runnable for running NotifyVsyncTimerOnMainThread on the
+      // main thread.
+      // TODO: On Linux Wayland, the vsync thread is currently the main thread,
+      // and yet we still dispatch the runnable. Do we need to?
+      bool useVsyncPriority = mozilla::BrowserTabsRemoteAutostart();
+      nsCOMPtr<nsIRunnable> vsyncEvent = new PrioritizableRunnable(
+          NS_NewRunnableFunction(
+              "RefreshDriverVsyncObserver::NotifyVsyncTimerOnMainThread",
+              [self = RefPtr{this}]() {
+                self->NotifyVsyncTimerOnMainThread();
+              }),
+          useVsyncPriority ? nsIRunnablePriority::PRIORITY_VSYNC
+                           : nsIRunnablePriority::PRIORITY_NORMAL);
+      NS_DispatchToMainThread(vsyncEvent);
+    }
+
+    void NotifyVsyncTimerOnMainThread() {
+      MOZ_ASSERT(NS_IsMainThread());
+
+      if (!mVsyncRefreshDriverTimer) {
+        // Ignore calls after Shutdown.
+        return;
+      }
+
+      VsyncEvent vsyncEvent;
+      {
+        // Get the last of the queued-up vsync notifications.
+        auto pendingVsync = mLastPendingVsyncNotification.Lock();
+        MOZ_RELEASE_ASSERT(
+            pendingVsync->isSome(),
+            "We should always have a pending vsync notification here.");
+        vsyncEvent = pendingVsync->extract();
+      }
+
+      // Call VsyncRefreshDriverTimer::NotifyVsyncOnMainThread, and keep a
+      // strong reference to it while calling the method.
+      RefPtr<VsyncRefreshDriverTimer> timer = mVsyncRefreshDriverTimer;
+      timer->NotifyVsyncOnMainThread(vsyncEvent);
+    }
+
+    void Shutdown() {
+      MOZ_ASSERT(NS_IsMainThread());
+      mVsyncRefreshDriverTimer = nullptr;
+    }
+
+   private:
+    ~RefreshDriverVsyncObserver() = default;
+
+    // VsyncRefreshDriverTimer holds this RefreshDriverVsyncObserver and it will
+    // be always available before Shutdown(). We can just use the raw pointer
+    // here.
+    // Only accessed on the main thread.
+    VsyncRefreshDriverTimer* mVsyncRefreshDriverTimer;
+
+    // Non-empty between a call to NotifyVsync and a call to
+    // NotifyVsyncOnMainThread. When multiple vsync notifications have been
+    // received between those two calls, this contains the last of the pending
+    // notifications. This is used both in the parent process and in the child
+    // process, but it only does something useful in the parent process. In the
+    // child process, both calls happen on the main thread right after one
+    // another, so there's only one notification to keep track of; vsync
+    // notification coalescing for child processes happens at the IPC level
+    // instead.
+    DataMutex<Maybe<VsyncEvent>> mLastPendingVsyncNotification;
+
+  };  // RefreshDriverVsyncObserver
+
+  VsyncRefreshDriverTimer(RefPtr<VsyncDispatcher>&& aVsyncDispatcher,
+                          RefPtr<VsyncMainChild>&& aVsyncChild)
+      : mVsyncDispatcher(aVsyncDispatcher),
+        mVsyncChild(aVsyncChild),
+        mVsyncRate(TimeDuration::Forever()),
+        mRecentVsync(TimeStamp::Now()),
+        mLastTickStart(TimeStamp::Now()),
+        mLastIdleTaskCount(0),
+        mLastRunOutOfMTTasksCount(0),
+        mProcessedVsync(true),
+        mHasPendingLowPrioTask(false) {
+    mVsyncObserver = new RefreshDriverVsyncObserver(this);
+  }
+
+  ~VsyncRefreshDriverTimer() override {
+    if (mVsyncDispatcher) {
+      mVsyncDispatcher->RemoveVsyncObserver(mVsyncObserver);
+      mVsyncDispatcher = nullptr;
+    } else if (mVsyncChild) {
+      mVsyncChild->RemoveChildRefreshTimer(mVsyncObserver);
+      mVsyncChild = nullptr;
+    }
+
+    // Detach current vsync timer from this VsyncObserver. The observer will no
+    // longer tick this timer.
+    mVsyncObserver->Shutdown();
+    mVsyncObserver = nullptr;
+  }
+
+  bool ShouldGiveNonVsyncTasksMoreTime(bool aCheckOnlyNewPendingTasks = false) {
+    TaskController* taskController = TaskController::Get();
+    IdleTaskManager* idleTaskManager = taskController->GetIdleTaskManager();
+    VsyncTaskManager* vsyncTaskManager = VsyncTaskManager::Get();
+
+    // Note, pendingTaskCount includes also all the pending idle and vsync
+    // tasks.
+    uint64_t pendingTaskCount =
+        taskController->PendingMainthreadTaskCountIncludingSuspended();
+    uint64_t pendingIdleTaskCount = idleTaskManager->PendingTaskCount();
+    uint64_t pendingVsyncTaskCount = vsyncTaskManager->PendingTaskCount();
+    if (!(pendingTaskCount > (pendingIdleTaskCount + pendingVsyncTaskCount))) {
+      return false;
+    }
+    if (aCheckOnlyNewPendingTasks) {
+      return true;
+    }
+
+    uint64_t idleTaskCount = idleTaskManager->ProcessedTaskCount();
+
+    // If we haven't processed new idle tasks and we have pending
+    // non-idle tasks, give those non-idle tasks more time,
+    // but only if the main thread wasn't totally empty at some point.
+    // In the parent process RunOutOfMTTasksCount() is less meaningful
+    // because some of the tasks run through AppShell.
+    return mLastIdleTaskCount == idleTaskCount &&
+           (taskController->RunOutOfMTTasksCount() ==
+                mLastRunOutOfMTTasksCount ||
+            XRE_IsParentProcess());
+  }
+
+  void NotifyVsyncOnMainThread(const VsyncEvent& aVsyncEvent) {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    mRecentVsync = aVsyncEvent.mTime;
+    mRecentVsyncId = aVsyncEvent.mId;
+    if (!mSuspendVsyncPriorityTicksUntil.IsNull() &&
+        mSuspendVsyncPriorityTicksUntil > TimeStamp::Now()) {
+      if (ShouldGiveNonVsyncTasksMoreTime()) {
+        if (!IsAnyToplevelContentPageLoading()) {
+          // If pages aren't loading and there aren't other tasks to run,
+          // trigger the pending vsync notification.
+          mPendingVsync = mRecentVsync;
+          mPendingVsyncId = mRecentVsyncId;
+          if (!mHasPendingLowPrioTask) {
+            mHasPendingLowPrioTask = true;
+            NS_DispatchToMainThreadQueue(
+                NS_NewRunnableFunction(
+                    "NotifyVsyncOnMainThread[low priority]",
+                    [self = RefPtr{this}]() {
+                      self->mHasPendingLowPrioTask = false;
+                      if (self->mRecentVsync == self->mPendingVsync &&
+                          self->mRecentVsyncId == self->mPendingVsyncId &&
+                          !self->ShouldGiveNonVsyncTasksMoreTime()) {
+                        self->mSuspendVsyncPriorityTicksUntil = TimeStamp();
+                        self->NotifyVsyncOnMainThread({self->mPendingVsyncId,
+                                                       self->mPendingVsync,
+                                                       /* unused */
+                                                       TimeStamp()});
+                      }
+                    }),
+                EventQueuePriority::Low);
+          }
+        }
+        return;
+      }
+
+      // Clear the value since we aren't blocking anymore because there aren't
+      // any non-idle tasks to process.
+      mSuspendVsyncPriorityTicksUntil = TimeStamp();
+    }
+
+    if (StaticPrefs::layout_lower_priority_refresh_driver_during_load() &&
+        ShouldGiveNonVsyncTasksMoreTime()) {
+      nsPresContext* pctx = GetPresContextForOnlyRefreshDriver();
+      if (pctx && pctx->HadFirstContentfulPaint() && pctx->Document() &&
+          pctx->Document()->GetReadyStateEnum() <
+              Document::READYSTATE_COMPLETE) {
+        nsPIDOMWindowInner* win = pctx->Document()->GetInnerWindow();
+        uint32_t frameRateMultiplier = pctx->GetNextFrameRateMultiplier();
+        if (!frameRateMultiplier) {
+          pctx->DidUseFrameRateMultiplier();
+        }
+        if (win && frameRateMultiplier) {
+          dom::Performance* perf = win->GetPerformance();
+          // Limit slower refresh rate to 5 seconds between the
+          // first contentful paint and page load.
+          if (perf &&
+              perf->Now() < StaticPrefs::page_load_deprioritization_period()) {
+            if (mProcessedVsync) {
+              mProcessedVsync = false;
+              TimeDuration rate = GetTimerRate();
+              uint32_t slowRate = static_cast<uint32_t>(rate.ToMilliseconds() *
+                                                        frameRateMultiplier);
+              pctx->DidUseFrameRateMultiplier();
+              nsCOMPtr<nsIRunnable> vsyncEvent = NewRunnableMethod<>(
+                  "VsyncRefreshDriverTimer::IdlePriorityNotify", this,
+                  &VsyncRefreshDriverTimer::IdlePriorityNotify);
+              NS_DispatchToCurrentThreadQueue(vsyncEvent.forget(), slowRate,
+                                              EventQueuePriority::Idle);
+            }
+            return;
+          }
+        }
+      }
+    }
+
+    TickRefreshDriver(aVsyncEvent.mId, aVsyncEvent.mTime);
+  }
+
+  void RecordTelemetryProbes(TimeStamp aVsyncTimestamp) {
+    MOZ_ASSERT(NS_IsMainThread());
+#ifndef ANDROID /* bug 1142079 */
+    if (XRE_IsParentProcess()) {
+      TimeDuration vsyncLatency = TimeStamp::Now() - aVsyncTimestamp;
+      uint32_t sample = (uint32_t)vsyncLatency.ToMilliseconds();
+      Telemetry::Accumulate(Telemetry::FX_REFRESH_DRIVER_CHROME_FRAME_DELAY_MS,
+                            sample);
+      Telemetry::Accumulate(
+          Telemetry::FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS, sample);
+    } else if (mVsyncRate != TimeDuration::Forever()) {
+      TimeDuration contentDelay =
+          (TimeStamp::Now() - mLastTickStart) - mVsyncRate;
+      if (contentDelay.ToMilliseconds() < 0) {
+        // Vsyncs are noisy and some can come at a rate quicker than
+        // the reported hardware rate. In those cases, consider that we have 0
+        // delay.
+        contentDelay = TimeDuration::FromMilliseconds(0);
+      }
+      uint32_t sample = (uint32_t)contentDelay.ToMilliseconds();
+      Telemetry::Accumulate(Telemetry::FX_REFRESH_DRIVER_CONTENT_FRAME_DELAY_MS,
+                            sample);
+      Telemetry::Accumulate(
+          Telemetry::FX_REFRESH_DRIVER_SYNC_SCROLL_FRAME_DELAY_MS, sample);
+    } else {
+      // Request the vsync rate which VsyncChild stored the last time it got a
+      // vsync notification.
+      mVsyncRate = mVsyncChild->GetVsyncRate();
+    }
+#endif
+  }
+
+  void OnTimerStart() {
+    mLastTickStart = TimeStamp::Now();
+    mLastTickEnd = TimeStamp();
+    mLastIdleTaskCount = 0;
+  }
+
+  void IdlePriorityNotify() {
+    if (mLastProcessedTick.IsNull() || mRecentVsync > mLastProcessedTick) {
+      // mSuspendVsyncPriorityTicksUntil is for high priority vsync
+      // notifications only.
+      mSuspendVsyncPriorityTicksUntil = TimeStamp();
+      TickRefreshDriver(mRecentVsyncId, mRecentVsync);
+    }
+
+    mProcessedVsync = true;
+  }
+
+  hal::PerformanceHintSession* GetPerformanceHintSession() {
+    // The ContentChild creates/destroys the PerformanceHintSession in response
+    // to the process' priority being foregrounded/backgrounded. We can only use
+    // this session when using a single vsync source for the process, otherwise
+    // these threads may be performing work for multiple
+    // VsyncRefreshDriverTimers and we will misreport the work duration.
+    const ContentChild* contentChild = ContentChild::GetSingleton();
+    if (contentChild && mVsyncChild) {
+      return contentChild->PerformanceHintSession();
+    }
+
+    return nullptr;
+  }
+
+  void TickRefreshDriver(VsyncId aId, TimeStamp aVsyncTimestamp) {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    RecordTelemetryProbes(aVsyncTimestamp);
+
+    TimeStamp tickStart = TimeStamp::Now();
+
+    const TimeDuration previousRate = mVsyncRate;
+    const TimeDuration rate = GetTimerRate();
+
+    hal::PerformanceHintSession* const performanceHintSession =
+        GetPerformanceHintSession();
+    if (performanceHintSession && rate != previousRate) {
+      performanceHintSession->UpdateTargetWorkDuration(
+          ContentChild::GetPerformanceHintTarget(rate));
+    }
+
+    if (TimeDuration::FromMilliseconds(nsRefreshDriver::DefaultInterval()) >
+        rate) {
+      sMostRecentHighRateVsync = tickStart;
+      sMostRecentHighRate = rate;
+    }
+
+    // On 32-bit Windows we sometimes get times where TimeStamp::Now() is not
+    // monotonic because the underlying system apis produce non-monontonic
+    // results. (bug 1306896)
+#if !defined(_WIN32)
+    MOZ_ASSERT(aVsyncTimestamp <= tickStart);
+#endif
+
+    bool shouldGiveNonVSyncTasksMoreTime = ShouldGiveNonVsyncTasksMoreTime();
+
+    // Set these variables before calling RunRefreshDrivers so that they are
+    // visible to any nested ticks.
+    mLastTickStart = tickStart;
+    mLastProcessedTick = aVsyncTimestamp;
+
+    RunRefreshDrivers(aId, aVsyncTimestamp);
+
+    TimeStamp tickEnd = TimeStamp::Now();
+
+    if (performanceHintSession) {
+      performanceHintSession->ReportActualWorkDuration(tickEnd - tickStart);
+    }
+
+    // Re-read mLastTickStart in case there was a nested tick inside this
+    // tick.
+    TimeStamp mostRecentTickStart = mLastTickStart;
+
+    // Let also non-RefreshDriver code to run at least for awhile if we have
+    // a mVsyncRefreshDriverTimer.
+    // Always give a tiny bit, 5% of the vsync interval, time outside the
+    // tick
+    // In case there are both normal tasks and RefreshDrivers are doing
+    // work, mSuspendVsyncPriorityTicksUntil will be set to a timestamp in the
+    // future where the period between the previous tick start
+    // (mostRecentTickStart) and the next tick needs to be at least the amount
+    // of work normal tasks and RefreshDrivers did together (minus short grace
+    // period).
+    TimeDuration gracePeriod = rate / int64_t(20);
+
+    if (shouldGiveNonVSyncTasksMoreTime && !mLastTickEnd.IsNull() &&
+        XRE_IsContentProcess() &&
+        // For RefreshDriver scheduling during page load there is currently
+        // idle priority based setup.
+        // XXX Consider to remove the page load specific code paths.
+        !IsAnyToplevelContentPageLoading()) {
+      // In case normal tasks are doing lots of work, we still want to paint
+      // every now and then, so only at maximum 4 * rate of work is counted
+      // here.
+      // If we're giving extra time for tasks outside a tick, try to
+      // ensure the next vsync after that period is handled, so subtract
+      // a grace period.
+      TimeDuration timeForOutsideTick = clamped(
+          tickStart - mLastTickEnd - gracePeriod, gracePeriod, rate * 4);
+      mSuspendVsyncPriorityTicksUntil = tickEnd + timeForOutsideTick;
+    } else if (ShouldGiveNonVsyncTasksMoreTime(true)) {
+      // We've got some new tasks, give them some extra time.
+      // This handles also the case when mLastTickEnd.IsNull() above and we
+      // should give some more time for non-vsync tasks.
+      mSuspendVsyncPriorityTicksUntil = tickEnd + gracePeriod;
+    } else {
+      mSuspendVsyncPriorityTicksUntil = mostRecentTickStart + gracePeriod;
+    }
+
+    mLastIdleTaskCount =
+        TaskController::Get()->GetIdleTaskManager()->ProcessedTaskCount();
+    mLastRunOutOfMTTasksCount = TaskController::Get()->RunOutOfMTTasksCount();
+    mLastTickEnd = tickEnd;
+  }
+
+  void StartTimer() override {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    mLastFireTime = TimeStamp::Now();
+    mLastFireId = VsyncId();
+
+    if (mVsyncDispatcher) {
+      mVsyncDispatcher->AddVsyncObserver(mVsyncObserver);
+    } else if (mVsyncChild) {
+      mVsyncChild->AddChildRefreshTimer(mVsyncObserver);
+      OnTimerStart();
+    }
+    mIsTicking = true;
+  }
+
+  void StopTimer() override {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    if (mVsyncDispatcher) {
+      mVsyncDispatcher->RemoveVsyncObserver(mVsyncObserver);
+    } else if (mVsyncChild) {
+      mVsyncChild->RemoveChildRefreshTimer(mVsyncObserver);
+    }
+    mIsTicking = false;
+  }
+
+ public:
+  bool IsTicking() const override { return mIsTicking; }
+
+ protected:
+  void ScheduleNextTick(TimeStamp aNowTime) override {
+    // Do nothing since we just wait for the next vsync from
+    // RefreshDriverVsyncObserver.
+  }
+
+  void RunRefreshDrivers(VsyncId aId, TimeStamp aTimeStamp) {
+    Tick(aId, aTimeStamp);
+    for (auto& driver : mContentRefreshDrivers) {
+      driver->FinishedVsyncTick();
+    }
+    for (auto& driver : mRootRefreshDrivers) {
+      driver->FinishedVsyncTick();
+    }
+  }
+
+  // Always non-null. Has a weak pointer to us and notifies us of vsync.
+  RefPtr<RefreshDriverVsyncObserver> mVsyncObserver;
+
+  // Used in the parent process. We register mVsyncObserver with it for the
+  // duration during which we want to receive vsync notifications. We also
+  // use it to query the current vsync rate.
+  RefPtr<VsyncDispatcher> mVsyncDispatcher;
+  // Used it the content process. We register mVsyncObserver with it for the
+  // duration during which we want to receive vsync notifications. The
+  // mVsyncChild will be always available before VsyncChild::ActorDestroy().
+  // After ActorDestroy(), StartTimer() and StopTimer() calls will be non-op.
+  RefPtr<VsyncMainChild> mVsyncChild;
+
+  TimeDuration mVsyncRate;
+  bool mIsTicking = false;
+
+  TimeStamp mRecentVsync;
+  VsyncId mRecentVsyncId;
+  // The local start time when RefreshDrivers' Tick was called last time.
+  TimeStamp mLastTickStart;
+  // The local end time of the last RefreshDrivers' tick.
+  TimeStamp mLastTickEnd;
+  // The number of idle tasks the main thread has processed. It is updated
+  // right after RefreshDrivers' tick.
+  uint64_t mLastIdleTaskCount;
+  // If there were no idle tasks, we need to check if the main event queue
+  // was totally empty at times.
+  uint64_t mLastRunOutOfMTTasksCount;
+  // Note, mLastProcessedTick stores the vsync timestamp, which may be coming
+  // from a different process.
+  TimeStamp mLastProcessedTick;
+  // mSuspendVsyncPriorityTicksUntil is used to block too high refresh rate in
+  // case the main thread has also other non-idle tasks to process.
+  // The timestamp is effectively mLastTickEnd + some duration.
+  TimeStamp mSuspendVsyncPriorityTicksUntil;
+  bool mProcessedVsync;
+
+  TimeStamp mPendingVsync;
+  VsyncId mPendingVsyncId;
+  bool mHasPendingLowPrioTask;
+};  // VsyncRefreshDriverTimer
+
+/**
+ * Since the content process takes some time to setup
+ * the vsync IPC connection, this timer is used
+ * during the intial startup process.
+ * During initial startup, the refresh drivers
+ * are ticked off this timer, and are swapped out once content
+ * vsync IPC connection is established.
+ */
+class StartupRefreshDriverTimer : public SimpleTimerBasedRefreshDriverTimer {
+ public:
+  explicit StartupRefreshDriverTimer(double aRate)
+      : SimpleTimerBasedRefreshDriverTimer(aRate) {}
+
+ protected:
+  void ScheduleNextTick(TimeStamp aNowTime) override {
+    // Since this is only used for startup, it isn't super critical
+    // that we tick at consistent intervals.
+    TimeStamp newTarget = aNowTime + mRateDuration;
+    uint32_t delay =
+        static_cast<uint32_t>((newTarget - aNowTime).ToMilliseconds());
+    mTimer->InitWithNamedFuncCallback(
+        TimerTick, this, delay, nsITimer::TYPE_ONE_SHOT,
+        "StartupRefreshDriverTimer::ScheduleNextTick");
+    mTargetTime = newTarget;
+  }
+
+ public:
+  bool IsTicking() const override { return true; }
+};
+
+/*
+ * A RefreshDriverTimer for inactive documents.  When a new refresh driver is
+ * added, the rate is reset to the base (normally 1s/1fps).  Every time
+ * it ticks, a single refresh driver is poked.  Once they have all been poked,
+ * the duration between ticks doubles, up to mDisableAfterMilliseconds.  At that
+ * point, the timer is quiet and doesn't tick (until something is added to it
+ * again).
+ *
+ * When a timer is removed, there is a possibility of another timer
+ * being skipped for one cycle.  We could avoid this by adjusting
+ * mNextDriverIndex in RemoveRefreshDriver, but there's little need to
+ * add that complexity.  All we want is for inactive drivers to tick
+ * at some point, but we don't care too much about how often.
+ */
+class InactiveRefreshDriverTimer final
+    : public SimpleTimerBasedRefreshDriverTimer {
+ public:
+  explicit InactiveRefreshDriverTimer(double aRate)
+      : SimpleTimerBasedRefreshDriverTimer(aRate),
+        mNextTickDuration(aRate),
+        mDisableAfterMilliseconds(-1.0),
+        mNextDriverIndex(0) {}
+
+  InactiveRefreshDriverTimer(double aRate, double aDisableAfterMilliseconds)
+      : SimpleTimerBasedRefreshDriverTimer(aRate),
+        mNextTickDuration(aRate),
+        mDisableAfterMilliseconds(aDisableAfterMilliseconds),
+        mNextDriverIndex(0) {}
+
+  void AddRefreshDriver(nsRefreshDriver* aDriver) override {
+    RefreshDriverTimer::AddRefreshDriver(aDriver);
+
+    LOG("[%p] inactive timer got new refresh driver %p, resetting rate", this,
+        aDriver);
+
+    // reset the timer, and start with the newly added one next time.
+    mNextTickDuration = mRateMilliseconds;
+
+    // we don't really have to start with the newly added one, but we may as
+    // well not tick the old ones at the fastest rate any more than we need to.
+    mNextDriverIndex = GetRefreshDriverCount() - 1;
+
+    StopTimer();
+    StartTimer();
+  }
+
+  TimeDuration GetTimerRate() override {
+    return TimeDuration::FromMilliseconds(mNextTickDuration);
+  }
+
+ protected:
+  uint32_t GetRefreshDriverCount() {
+    return mContentRefreshDrivers.Length() + mRootRefreshDrivers.Length();
+  }
+
+  void StartTimer() override {
+    mLastFireTime = TimeStamp::Now();
+    mLastFireId = VsyncId();
+
+    mTargetTime = mLastFireTime + mRateDuration;
+
+    uint32_t delay = static_cast<uint32_t>(mRateMilliseconds);
+    mTimer->InitWithNamedFuncCallback(TimerTickOne, this, delay,
+                                      nsITimer::TYPE_ONE_SHOT,
+                                      "InactiveRefreshDriverTimer::StartTimer");
+    mIsTicking = true;
+  }
+
+  void StopTimer() override {
+    mTimer->Cancel();
+    mIsTicking = false;
+  }
+
+  void ScheduleNextTick(TimeStamp aNowTime) override {
+    if (mDisableAfterMilliseconds > 0.0 &&
+        mNextTickDuration > mDisableAfterMilliseconds) {
+      // We hit the time after which we should disable
+      // inactive window refreshes; don't schedule anything
+      // until we get kicked by an AddRefreshDriver call.
+      return;
+    }
+
+    // double the next tick time if we've already gone through all of them once
+    if (mNextDriverIndex >= GetRefreshDriverCount()) {
+      mNextTickDuration *= 2.0;
+      mNextDriverIndex = 0;
+    }
+
+    // this doesn't need to be precise; do a simple schedule
+    uint32_t delay = static_cast<uint32_t>(mNextTickDuration);
+    mTimer->InitWithNamedFuncCallback(
+        TimerTickOne, this, delay, nsITimer::TYPE_ONE_SHOT,
+        "InactiveRefreshDriverTimer::ScheduleNextTick");
+
+    LOG("[%p] inactive timer next tick in %f ms [index %d/%d]", this,
+        mNextTickDuration, mNextDriverIndex, GetRefreshDriverCount());
+  }
+
+ public:
+  bool IsTicking() const override { return mIsTicking; }
+
+ protected:
+  /* Runs just one driver's tick. */
+  void TickOne() {
+    TimeStamp now = TimeStamp::Now();
+
+    ScheduleNextTick(now);
+
+    mLastFireTime = now;
+    mLastFireId = VsyncId();
+
+    nsTArray<RefPtr<nsRefreshDriver>> drivers(mContentRefreshDrivers.Clone());
+    drivers.AppendElements(mRootRefreshDrivers);
+    size_t index = mNextDriverIndex;
+
+    if (index < drivers.Length() &&
+        !drivers[index]->IsTestControllingRefreshesEnabled()) {
+      TickDriver(drivers[index], VsyncId(), now);
+    }
+
+    mNextDriverIndex++;
+  }
+
+  static void TimerTickOne(nsITimer* aTimer, void* aClosure) {
+    RefPtr<InactiveRefreshDriverTimer> timer =
+        static_cast<InactiveRefreshDriverTimer*>(aClosure);
+    timer->TickOne();
+  }
+
+  double mNextTickDuration;
+  double mDisableAfterMilliseconds;
+  uint32_t mNextDriverIndex;
+  bool mIsTicking = false;
+};
+
+}  // namespace mozilla
+
+static StaticRefPtr<RefreshDriverTimer> sRegularRateTimer;
+static StaticAutoPtr<nsTArray<RefreshDriverTimer*>> sRegularRateTimerList;
+static StaticRefPtr<InactiveRefreshDriverTimer> sThrottledRateTimer;
+
+void nsRefreshDriver::CreateVsyncRefreshTimer() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (gfxPlatform::IsInLayoutAsapMode()) {
+    return;
+  }
+
+  if (!mOwnTimer) {
+    // If available, we fetch the widget-specific vsync source.
+    nsPresContext* pc = GetPresContext();
+    nsCOMPtr<nsIWidget> widget = pc->GetRootWidget();
+    if (widget) {
+      if (RefPtr<VsyncDispatcher> vsyncDispatcher =
+              widget->GetVsyncDispatcher()) {
+        mOwnTimer = VsyncRefreshDriverTimer::
+            CreateForParentProcessWithLocalVsyncDispatcher(
+                std::move(vsyncDispatcher));
+        sRegularRateTimerList->AppendElement(mOwnTimer.get());
+        return;
+      }
+      if (BrowserChild* browserChild = widget->GetOwningBrowserChild()) {
+        if (RefPtr<VsyncMainChild> vsyncChildViaPBrowser =
+                browserChild->GetVsyncChild()) {
+          mOwnTimer = VsyncRefreshDriverTimer::CreateForContentProcess(
+              std::move(vsyncChildViaPBrowser));
+          sRegularRateTimerList->AppendElement(mOwnTimer.get());
+          return;
+        }
+      }
+    }
+  }
+  if (!sRegularRateTimer) {
+    if (XRE_IsParentProcess()) {
+      // Make sure all vsync systems are ready.
+      gfxPlatform::GetPlatform();
+      // In parent process, we can create the VsyncRefreshDriverTimer directly.
+      sRegularRateTimer =
+          VsyncRefreshDriverTimer::CreateForParentProcessWithGlobalVsync();
+    } else {
+      PBackgroundChild* actorChild =
+          BackgroundChild::GetOrCreateForCurrentThread();
+      if (NS_WARN_IF(!actorChild)) {
+        return;
+      }
+
+      auto vsyncChildViaPBackground = MakeRefPtr<dom::VsyncMainChild>();
+      dom::PVsyncChild* actor =
+          actorChild->SendPVsyncConstructor(vsyncChildViaPBackground);
+      if (NS_WARN_IF(!actor)) {
+        return;
+      }
+
+      RefPtr<RefreshDriverTimer> vsyncRefreshDriverTimer =
+          VsyncRefreshDriverTimer::CreateForContentProcess(
+              std::move(vsyncChildViaPBackground));
+
+      sRegularRateTimer = std::move(vsyncRefreshDriverTimer);
+    }
+  }
+}
+
+static uint32_t GetFirstFrameDelay(imgIRequest* req) {
+  nsCOMPtr<imgIContainer> container;
+  if (NS_FAILED(req->GetImage(getter_AddRefs(container))) || !container) {
+    return 0;
+  }
+
+  // If this image isn't animated, there isn't a first frame delay.
+  int32_t delay = container->GetFirstFrameDelay();
+  if (delay < 0) return 0;
+
+  return static_cast<uint32_t>(delay);
+}
+
+/* static */
+void nsRefreshDriver::Shutdown() {
+  MOZ_ASSERT(NS_IsMainThread());
+  // clean up our timers
+  sRegularRateTimer = nullptr;
+  sRegularRateTimerList = nullptr;
+  sThrottledRateTimer = nullptr;
+}
+
+/* static */
+int32_t nsRefreshDriver::DefaultInterval() {
+  return NSToIntRound(1000.0 / gfxPlatform::GetDefaultFrameRate());
+}
+
+/* static */
+double nsRefreshDriver::HighRateMultiplier() {
+  // We're in high rate mode if we've gotten a fast rate during the last
+  // DefaultInterval().
+  bool inHighRateMode =
+      !gfxPlatform::IsInLayoutAsapMode() &&
+      StaticPrefs::layout_expose_high_rate_mode_from_refreshdriver() &&
+      !sMostRecentHighRateVsync.IsNull() &&
+      (sMostRecentHighRateVsync +
+       TimeDuration::FromMilliseconds(DefaultInterval())) > TimeStamp::Now();
+  if (!inHighRateMode) {
+    // Clear the timestamp so that the next call is faster.
+    sMostRecentHighRateVsync = TimeStamp();
+    sMostRecentHighRate = TimeDuration();
+    return 1.0;
+  }
+
+  return sMostRecentHighRate.ToMilliseconds() / DefaultInterval();
+}
+
+// Compute the interval to use for the refresh driver timer, in milliseconds.
+// outIsDefault indicates that rate was not explicitly set by the user
+// so we might choose other, more appropriate rates (e.g. vsync, etc)
+// layout.frame_rate=0 indicates "ASAP mode".
+// In ASAP mode rendering is iterated as fast as possible (typically for stress
+// testing). A target rate of 10k is used internally instead of special-handling
+// 0. Backends which block on swap/present/etc should try to not block when
+// layout.frame_rate=0 - to comply with "ASAP" as much as possible.
+double nsRefreshDriver::GetRegularTimerInterval() const {
+  int32_t rate = Preferences::GetInt("layout.frame_rate", -1);
+  if (rate < 0) {
+    rate = gfxPlatform::GetDefaultFrameRate();
+  } else if (rate == 0) {
+    rate = 10000;
+  }
+
+  return 1000.0 / rate;
+}
+
+/* static */
+double nsRefreshDriver::GetThrottledTimerInterval() {
+  uint32_t rate = StaticPrefs::layout_throttled_frame_rate();
+  return 1000.0 / rate;
+}
+
+/* static */
+TimeDuration nsRefreshDriver::GetMinRecomputeVisibilityInterval() {
+  return TimeDuration::FromMilliseconds(
+      StaticPrefs::layout_visibility_min_recompute_interval_ms());
+}
+
+RefreshDriverTimer* nsRefreshDriver::ChooseTimer() {
+  if (mThrottled) {
+    if (!sThrottledRateTimer) {
+      sThrottledRateTimer = new InactiveRefreshDriverTimer(
+          GetThrottledTimerInterval(),
+          DEFAULT_INACTIVE_TIMER_DISABLE_SECONDS * 1000.0);
+    }
+    return sThrottledRateTimer;
+  }
+
+  if (!mOwnTimer) {
+    CreateVsyncRefreshTimer();
+  }
+
+  if (mOwnTimer) {
+    return mOwnTimer.get();
+  }
+
+  if (!sRegularRateTimer) {
+    double rate = GetRegularTimerInterval();
+    sRegularRateTimer = new StartupRefreshDriverTimer(rate);
+  }
+
+  return sRegularRateTimer;
+}
+
+static nsDocShell* GetDocShell(nsPresContext* aPresContext) {
+  if (!aPresContext) {
+    return nullptr;
+  }
+  return static_cast<nsDocShell*>(aPresContext->GetDocShell());
+}
+
+nsRefreshDriver::nsRefreshDriver(nsPresContext* aPresContext)
+    : mActiveTimer(nullptr),
+      mOwnTimer(nullptr),
+      mPresContext(aPresContext),
+      mRootRefresh(nullptr),
+      mNextTransactionId{0},
+      mFreezeCount(0),
+      mThrottledFrameRequestInterval(
+          TimeDuration::FromMilliseconds(GetThrottledTimerInterval())),
+      mMinRecomputeVisibilityInterval(GetMinRecomputeVisibilityInterval()),
+      mThrottled(false),
+      mNeedToRecomputeVisibility(false),
+      mTestControllingRefreshes(false),
+      mViewManagerFlushIsPending(false),
+      mHasScheduleFlush(false),
+      mInRefresh(false),
+      mWaitingForTransaction(false),
+      mSkippedPaints(false),
+      mResizeSuppressed(false),
+      mNotifyDOMContentFlushed(false),
+      mNeedToUpdateIntersectionObservations(false),
+      mNeedToUpdateResizeObservers(false),
+      mMightNeedMediaQueryListenerUpdate(false),
+      mNeedToUpdateContentRelevancy(false),
+      mInNormalTick(false),
+      mAttemptedExtraTickSinceLastVsync(false),
+      mHasExceededAfterLoadTickPeriod(false),
+      mHasStartedTimerAtLeastOnce(false) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(mPresContext,
+             "Need a pres context to tell us to call Disconnect() later "
+             "and decrement sRefreshDriverCount.");
+  mMostRecentRefresh = TimeStamp::Now();
+  mNextThrottledFrameRequestTick = mMostRecentRefresh;
+  mNextRecomputeVisibilityTick = mMostRecentRefresh;
+
+  if (!sRegularRateTimerList) {
+    sRegularRateTimerList = new nsTArray<RefreshDriverTimer*>();
+  }
+  ++sRefreshDriverCount;
+}
+
+nsRefreshDriver::~nsRefreshDriver() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(ObserverCount() == mEarlyRunners.Length(),
+             "observers, except pending selection scrolls, "
+             "should have been unregistered");
+  MOZ_ASSERT(!mActiveTimer, "timer should be gone");
+  MOZ_ASSERT(!mPresContext,
+             "Should have called Disconnect() and decremented "
+             "sRefreshDriverCount!");
+
+  if (mRootRefresh) {
+    mRootRefresh->RemoveRefreshObserver(this, FlushType::Style);
+    mRootRefresh = nullptr;
+  }
+  if (mOwnTimer && sRegularRateTimerList) {
+    sRegularRateTimerList->RemoveElement(mOwnTimer.get());
+  }
+}
+
+// Method for testing.  See nsIDOMWindowUtils.advanceTimeAndRefresh
+// for description.
+void nsRefreshDriver::AdvanceTimeAndRefresh(int64_t aMilliseconds) {
+  // ensure that we're removed from our driver
+  StopTimer();
+
+  if (!mTestControllingRefreshes) {
+    mMostRecentRefresh = TimeStamp::Now();
+
+    mTestControllingRefreshes = true;
+    if (mWaitingForTransaction) {
+      // Disable any refresh driver throttling when entering test mode
+      mWaitingForTransaction = false;
+      mSkippedPaints = false;
+    }
+  }
+
+  mMostRecentRefresh += TimeDuration::FromMilliseconds((double)aMilliseconds);
+
+  mozilla::dom::AutoNoJSAPI nojsapi;
+  DoTick();
+}
+
+void nsRefreshDriver::RestoreNormalRefresh() {
+  mTestControllingRefreshes = false;
+  EnsureTimerStarted(eAllowTimeToGoBackwards);
+  mPendingTransactions.Clear();
+}
+
+TimeStamp nsRefreshDriver::MostRecentRefresh(bool aEnsureTimerStarted) const {
+  // In case of stylo traversal, we have already activated the refresh driver in
+  // RestyleManager::ProcessPendingRestyles().
+  if (aEnsureTimerStarted && !ServoStyleSet::IsInServoTraversal()) {
+    const_cast<nsRefreshDriver*>(this)->EnsureTimerStarted();
+  }
+
+  return mMostRecentRefresh;
+}
+
+void nsRefreshDriver::AddRefreshObserver(nsARefreshObserver* aObserver,
+                                         FlushType aFlushType,
+                                         const char* aObserverDescription) {
+  ObserverArray& array = ArrayFor(aFlushType);
+  MOZ_ASSERT(!array.Contains(aObserver),
+             "We don't want to redundantly register the same observer");
+  array.AppendElement(
+      ObserverData{aObserver, aObserverDescription, TimeStamp::Now(),
+                   MarkerInnerWindowIdFromDocShell(GetDocShell(mPresContext)),
+                   profiler_capture_backtrace(), aFlushType});
+#ifdef DEBUG
+  MOZ_ASSERT(aObserver->mRegistrationCount >= 0,
+             "Registration count shouldn't be able to go negative");
+  aObserver->mRegistrationCount++;
+#endif
+  EnsureTimerStarted();
+}
+
+bool nsRefreshDriver::RemoveRefreshObserver(nsARefreshObserver* aObserver,
+                                            FlushType aFlushType) {
+  ObserverArray& array = ArrayFor(aFlushType);
+  auto index = array.IndexOf(aObserver);
+  if (index == ObserverArray::array_type::NoIndex) {
+    return false;
+  }
+
+  if (profiler_thread_is_being_profiled_for_markers()) {
+    auto& data = array.ElementAt(index);
+    nsPrintfCString str("%s [%s]", data.mDescription,
+                        kFlushTypeNames[aFlushType]);
+    PROFILER_MARKER_TEXT(
+        "RefreshObserver", GRAPHICS,
+        MarkerOptions(MarkerStack::TakeBacktrace(std::move(data.mCause)),
+                      MarkerTiming::IntervalUntilNowFrom(data.mRegisterTime),
+                      std::move(data.mInnerWindowId)),
+        str);
+  }
+
+  array.RemoveElementAt(index);
+#ifdef DEBUG
+  aObserver->mRegistrationCount--;
+  MOZ_ASSERT(aObserver->mRegistrationCount >= 0,
+             "Registration count shouldn't be able to go negative");
+#endif
+  return true;
+}
+
+void nsRefreshDriver::AddTimerAdjustmentObserver(
+    nsATimerAdjustmentObserver* aObserver) {
+  MOZ_ASSERT(!mTimerAdjustmentObservers.Contains(aObserver));
+  mTimerAdjustmentObservers.AppendElement(aObserver);
+}
+
+void nsRefreshDriver::RemoveTimerAdjustmentObserver(
+    nsATimerAdjustmentObserver* aObserver) {
+  MOZ_ASSERT(mTimerAdjustmentObservers.Contains(aObserver));
+  mTimerAdjustmentObservers.RemoveElement(aObserver);
+}
+
+void nsRefreshDriver::PostVisualViewportResizeEvent(
+    VVPResizeEvent* aResizeEvent) {
+  mVisualViewportResizeEvents.AppendElement(aResizeEvent);
+  EnsureTimerStarted();
+}
+
+void nsRefreshDriver::DispatchVisualViewportResizeEvents() {
+  // We're taking a hint from scroll events and only dispatch the current set
+  // of queued resize events. If additional events are posted in response to
+  // the current events being dispatched, we'll dispatch them on the next tick.
+  VisualViewportResizeEventArray events =
+      std::move(mVisualViewportResizeEvents);
+  for (auto& event : events) {
+    event->Run();
+  }
+}
+
+void nsRefreshDriver::PostScrollEvent(mozilla::Runnable* aScrollEvent,
+                                      bool aDelayed) {
+  if (aDelayed) {
+    mDelayedScrollEvents.AppendElement(aScrollEvent);
+  } else {
+    mScrollEvents.AppendElement(aScrollEvent);
+    EnsureTimerStarted();
+  }
+}
+
+void nsRefreshDriver::DispatchScrollEvents() {
+  // Scroll events are one-shot, so after running them we can drop them.
+  // However, dispatching a scroll event can potentially cause more scroll
+  // events to be posted, so we move the initial set into a temporary array
+  // first. (Newly posted scroll events will be dispatched on the next tick.)
+  ScrollEventArray events = std::move(mScrollEvents);
+  for (auto& event : events) {
+    event->Run();
+  }
+}
+
+void nsRefreshDriver::PostVisualViewportScrollEvent(
+    VVPScrollEvent* aScrollEvent) {
+  mVisualViewportScrollEvents.AppendElement(aScrollEvent);
+  EnsureTimerStarted();
+}
+
+void nsRefreshDriver::DispatchVisualViewportScrollEvents() {
+  // Scroll events are one-shot, so after running them we can drop them.
+  // However, dispatching a scroll event can potentially cause more scroll
+  // events to be posted, so we move the initial set into a temporary array
+  // first. (Newly posted scroll events will be dispatched on the next tick.)
+  VisualViewportScrollEventArray events =
+      std::move(mVisualViewportScrollEvents);
+  for (auto& event : events) {
+    event->Run();
+  }
+}
+
+// https://drafts.csswg.org/cssom-view/#evaluate-media-queries-and-report-changes
+void nsRefreshDriver::EvaluateMediaQueriesAndReportChanges() {
+  if (!mMightNeedMediaQueryListenerUpdate) {
+    return;
+  }
+  mMightNeedMediaQueryListenerUpdate = false;
+  if (!mPresContext) {
+    return;
+  }
+  AUTO_PROFILER_LABEL_RELEVANT_FOR_JS(
+      "Evaluate media queries and report changes", LAYOUT);
+  RefPtr<Document> doc = mPresContext->Document();
+  doc->EvaluateMediaQueriesAndReportChanges(/* aRecurse = */ true);
+}
+
+void nsRefreshDriver::AddPostRefreshObserver(
+    nsAPostRefreshObserver* aObserver) {
+  MOZ_ASSERT(!mPostRefreshObservers.Contains(aObserver));
+  mPostRefreshObservers.AppendElement(aObserver);
+}
+
+void nsRefreshDriver::RemovePostRefreshObserver(
+    nsAPostRefreshObserver* aObserver) {
+  bool removed = mPostRefreshObservers.RemoveElement(aObserver);
+  MOZ_DIAGNOSTIC_ASSERT(removed);
+  Unused << removed;
+}
+
+void nsRefreshDriver::AddImageRequest(imgIRequest* aRequest) {
+  uint32_t delay = GetFirstFrameDelay(aRequest);
+  if (delay == 0) {
+    mRequests.Insert(aRequest);
+  } else {
+    auto* const start = mStartTable.GetOrInsertNew(delay);
+    start->mEntries.Insert(aRequest);
+  }
+
+  EnsureTimerStarted();
+
+  if (profiler_thread_is_being_profiled_for_markers()) {
+    nsCOMPtr<nsIURI> uri = aRequest->GetURI();
+
+    PROFILER_MARKER_TEXT("Image Animation", GRAPHICS,
+                         MarkerOptions(MarkerTiming::IntervalStart(),
+                                       MarkerInnerWindowIdFromDocShell(
+                                           GetDocShell(mPresContext))),
+                         nsContentUtils::TruncatedURLForDisplay(uri));
+  }
+}
+
+void nsRefreshDriver::RemoveImageRequest(imgIRequest* aRequest) {
+  // Try to remove from both places, just in case.
+  bool removed = mRequests.EnsureRemoved(aRequest);
+  uint32_t delay = GetFirstFrameDelay(aRequest);
+  if (delay != 0) {
+    ImageStartData* start = mStartTable.Get(delay);
+    if (start) {
+      removed = removed | start->mEntries.EnsureRemoved(aRequest);
+    }
+  }
+
+  if (removed && profiler_thread_is_being_profiled_for_markers()) {
+    nsCOMPtr<nsIURI> uri = aRequest->GetURI();
+
+    PROFILER_MARKER_TEXT("Image Animation", GRAPHICS,
+                         MarkerOptions(MarkerTiming::IntervalEnd(),
+                                       MarkerInnerWindowIdFromDocShell(
+                                           GetDocShell(mPresContext))),
+                         nsContentUtils::TruncatedURLForDisplay(uri));
+  }
+}
+
+void nsRefreshDriver::NotifyDOMContentLoaded() {
+  // If the refresh driver is going to tick, we mark the timestamp after
+  // everything is flushed in the next tick. If it isn't, mark ourselves as
+  // flushed now.
+  if (!HasObservers()) {
+    if (nsPresContext* pc = GetPresContext()) {
+      pc->NotifyDOMContentFlushed();
+    }
+    // else, we don't have a nsPresContext, so our doc is probably being
+    // destroyed and this notification doesn't need sending anyway.
+  } else {
+    mNotifyDOMContentFlushed = true;
+  }
+}
+
+void nsRefreshDriver::RegisterCompositionPayload(
+    const mozilla::layers::CompositionPayload& aPayload) {
+  mCompositionPayloads.AppendElement(aPayload);
+}
+
+void nsRefreshDriver::AddForceNotifyContentfulPaintPresContext(
+    nsPresContext* aPresContext) {
+  mForceNotifyContentfulPaintPresContexts.AppendElement(aPresContext);
+}
+
+void nsRefreshDriver::FlushForceNotifyContentfulPaintPresContext() {
+  while (!mForceNotifyContentfulPaintPresContexts.IsEmpty()) {
+    WeakPtr<nsPresContext> presContext =
+        mForceNotifyContentfulPaintPresContexts.PopLastElement();
+    if (presContext) {
+      presContext->NotifyContentfulPaint();
+    }
+  }
+}
+
+void nsRefreshDriver::RunDelayedEventsSoon() {
+  // Place entries for delayed events into their corresponding normal list,
+  // and schedule a refresh. When these delayed events run, if their document
+  // still has events suppressed then they will be readded to the delayed
+  // events list.
+
+  mScrollEvents.AppendElements(mDelayedScrollEvents);
+  mDelayedScrollEvents.Clear();
+
+  mResizeEventFlushObservers.AppendElements(mDelayedResizeEventFlushObservers);
+  mDelayedResizeEventFlushObservers.Clear();
+
+  EnsureTimerStarted();
+}
+
+bool nsRefreshDriver::CanDoCatchUpTick() {
+  if (mTestControllingRefreshes || !mActiveTimer) {
+    return false;
+  }
+
+  // If we've already ticked for the current timer refresh (or more recently
+  // than that), then we don't need to do any catching up.
+  if (mMostRecentRefresh >= mActiveTimer->MostRecentRefresh()) {
+    return false;
+  }
+
+  if (mActiveTimer->IsBlocked()) {
+    return false;
+  }
+
+  if (mTickVsyncTime.IsNull()) {
+    // Don't try to run a catch-up tick before there has been at least one
+    // normal tick. The catch-up tick could negatively affect page load
+    // performance.
+    return false;
+  }
+
+  if (mPresContext && mPresContext->Document()->GetReadyStateEnum() <
+                          Document::READYSTATE_COMPLETE) {
+    // Don't try to run a catch-up tick before the page has finished loading.
+    // The catch-up tick could negatively affect page load performance.
+    return false;
+  }
+
+  return true;
+}
+
+bool nsRefreshDriver::CanDoExtraTick() {
+  // Only allow one extra tick per normal vsync tick.
+  if (mAttemptedExtraTickSinceLastVsync) {
+    return false;
+  }
+
+  // If we don't have a timer, or we didn't tick on the timer's
+  // refresh then we can't do an 'extra' tick (but we may still
+  // do a catch up tick).
+  if (!mActiveTimer ||
+      mActiveTimer->MostRecentRefresh() != mMostRecentRefresh) {
+    return false;
+  }
+
+  // Grab the current timestamp before checking the tick hint to be sure
+  // sure that it's equal or smaller than the value used within checking
+  // the tick hint.
+  TimeStamp now = TimeStamp::Now();
+  Maybe<TimeStamp> nextTick = mActiveTimer->GetNextTickHint();
+  int32_t minimumRequiredTime = StaticPrefs::layout_extra_tick_minimum_ms();
+  // If there's less than 4 milliseconds until the next tick, it's probably
+  // not worth trying to catch up.
+  if (minimumRequiredTime < 0 || !nextTick ||
+      (*nextTick - now) < TimeDuration::FromMilliseconds(minimumRequiredTime)) {
+    return false;
+  }
+
+  return true;
+}
+
+void nsRefreshDriver::EnsureTimerStarted(EnsureTimerStartedFlags aFlags) {
+  // FIXME: Bug 1346065: We should also assert the case where we have no
+  // stylo-threads.
+  MOZ_ASSERT(!ServoStyleSet::IsInServoTraversal() || NS_IsMainThread(),
+             "EnsureTimerStarted should be called only when we are not "
+             "in servo traversal or on the main-thread");
+
+  if (mTestControllingRefreshes) return;
+
+  if (!mRefreshTimerStartedCause) {
+    mRefreshTimerStartedCause = profiler_capture_backtrace();
+  }
+
+  // will it already fire, and no other changes needed?
+  if (mActiveTimer && !(aFlags & eForceAdjustTimer)) {
+    // If we're being called from within a user input handler, and we think
+    // there's time to rush an extra tick immediately, then schedule a runnable
+    // to run the extra tick.
+    if (mUserInputProcessingCount && CanDoExtraTick()) {
+      RefPtr<nsRefreshDriver> self = this;
+      NS_DispatchToCurrentThreadQueue(
+          NS_NewRunnableFunction(
+              "RefreshDriver::EnsureTimerStarted::extra",
+              [self]() -> void {
+                // Re-check if we can still do an extra tick, in case anything
+                // changed while the runnable was pending.
+                if (self->CanDoExtraTick()) {
+                  PROFILER_MARKER_UNTYPED("ExtraRefreshDriverTick", GRAPHICS);
+                  LOG("[%p] Doing extra tick for user input", self.get());
+                  self->mAttemptedExtraTickSinceLastVsync = true;
+                  self->Tick(self->mActiveTimer->MostRecentRefreshVsyncId(),
+                             self->mActiveTimer->MostRecentRefresh(),
+                             IsExtraTick::Yes);
+                }
+              }),
+          EventQueuePriority::Vsync);
+    }
+    return;
+  }
+
+  if (IsFrozen() || !mPresContext) {
+    // If we don't want to start it now, or we've been disconnected.
+    StopTimer();
+    return;
+  }
+
+  if (mPresContext->Document()->IsBeingUsedAsImage()) {
+    // Image documents receive ticks from clients' refresh drivers.
+    // XXXdholbert Exclude SVG-in-opentype fonts from this optimization, until
+    // they receive refresh-driver ticks from their client docs (bug 1107252).
+    if (!mPresContext->Document()->IsSVGGlyphsDocument()) {
+      MOZ_ASSERT(!mActiveTimer,
+                 "image doc refresh driver should never have its own timer");
+      return;
+    }
+  }
+
+  // We got here because we're either adjusting the time *or* we're
+  // starting it for the first time.  Add to the right timer,
+  // prehaps removing it from a previously-set one.
+  RefreshDriverTimer* newTimer = ChooseTimer();
+  if (newTimer != mActiveTimer) {
+    if (mActiveTimer) mActiveTimer->RemoveRefreshDriver(this);
+    mActiveTimer = newTimer;
+    mActiveTimer->AddRefreshDriver(this);
+
+    if (!mHasStartedTimerAtLeastOnce) {
+      mHasStartedTimerAtLeastOnce = true;
+      if (profiler_thread_is_being_profiled_for_markers()) {
+        nsCString text = "initial timer start "_ns;
+        if (mPresContext->Document()->GetDocumentURI()) {
+          text.Append(nsContentUtils::TruncatedURLForDisplay(
+              mPresContext->Document()->GetDocumentURI()));
+        }
+
+        PROFILER_MARKER_TEXT("nsRefreshDriver", LAYOUT,
+                             MarkerOptions(MarkerInnerWindowIdFromDocShell(
+                                 GetDocShell(mPresContext))),
+                             text);
+      }
+    }
+
+    // If the timer has ticked since we last ticked, consider doing a 'catch-up'
+    // tick immediately.
+    if (CanDoCatchUpTick()) {
+      RefPtr<nsRefreshDriver> self = this;
+      NS_DispatchToCurrentThreadQueue(
+          NS_NewRunnableFunction(
+              "RefreshDriver::EnsureTimerStarted::catch-up",
+              [self]() -> void {
+                // Re-check if we can still do a catch-up, in case anything
+                // changed while the runnable was pending.
+                if (self->CanDoCatchUpTick()) {
+                  LOG("[%p] Doing catch up tick", self.get());
+                  self->Tick(self->mActiveTimer->MostRecentRefreshVsyncId(),
+                             self->mActiveTimer->MostRecentRefresh());
+                }
+              }),
+          EventQueuePriority::Vsync);
+    }
+  }
+
+  // When switching from an inactive timer to an active timer, the root
+  // refresh driver is skipped due to being set to the content refresh
+  // driver's timestamp. In case of EnsureTimerStarted is called from
+  // ScheduleViewManagerFlush, we should avoid this behavior to flush
+  // a paint in the same tick on the root refresh driver.
+  if (aFlags & eNeverAdjustTimer) {
+    return;
+  }
+
+  // Since the different timers are sampled at different rates, when switching
+  // timers, the most recent refresh of the new timer may be *before* the
+  // most recent refresh of the old timer.
+  // If we are restoring the refresh driver from test control, the time is
+  // expected to go backwards (see bug 1043078), otherwise we just keep the most
+  // recent tick of this driver (which may be older than the most recent tick of
+  // the timer).
+  if (!(aFlags & eAllowTimeToGoBackwards)) {
+    return;
+  }
+
+  if (mMostRecentRefresh != mActiveTimer->MostRecentRefresh()) {
+    mMostRecentRefresh = mActiveTimer->MostRecentRefresh();
+
+    for (nsATimerAdjustmentObserver* obs :
+         mTimerAdjustmentObservers.EndLimitedRange()) {
+      obs->NotifyTimerAdjusted(mMostRecentRefresh);
+    }
+  }
+}
+
+void nsRefreshDriver::StopTimer() {
+  if (!mActiveTimer) return;
+
+  mActiveTimer->RemoveRefreshDriver(this);
+  mActiveTimer = nullptr;
+  mRefreshTimerStartedCause = nullptr;
+}
+
+uint32_t nsRefreshDriver::ObserverCount() const {
+  uint32_t sum = 0;
+  for (const ObserverArray& array : mObservers) {
+    sum += array.Length();
+  }
+
+  // Even while throttled, we need to process layout and style changes.  Style
+  // changes can trigger transitions which fire events when they complete, and
+  // layout changes can affect media queries on child documents, triggering
+  // style changes, etc.
+  sum += mAnimationEventFlushObservers.Length();
+  sum += mResizeEventFlushObservers.Length();
+  sum += mStyleFlushObservers.Length();
+  sum += mLayoutFlushObservers.Length();
+  sum += mPendingFullscreenEvents.Length();
+  sum += mFrameRequestCallbackDocs.Length();
+  sum += mThrottledFrameRequestCallbackDocs.Length();
+  sum += mViewManagerFlushIsPending;
+  sum += mEarlyRunners.Length();
+  sum += mTimerAdjustmentObservers.Length();
+  sum += mAutoFocusFlushDocuments.Length();
+  return sum;
+}
+
+bool nsRefreshDriver::HasObservers() const {
+  for (const ObserverArray& array : mObservers) {
+    if (!array.IsEmpty()) {
+      return true;
+    }
+  }
+
+  // We should NOT count mTimerAdjustmentObservers here since this method is
+  // used to determine whether or not to stop the timer or re-start it and timer
+  // adjustment observers should not influence timer starting or stopping.
+  return (mViewManagerFlushIsPending && !mThrottled) ||
+         !mStyleFlushObservers.IsEmpty() || !mLayoutFlushObservers.IsEmpty() ||
+         !mAnimationEventFlushObservers.IsEmpty() ||
+         !mResizeEventFlushObservers.IsEmpty() ||
+         !mPendingFullscreenEvents.IsEmpty() ||
+         !mFrameRequestCallbackDocs.IsEmpty() ||
+         !mThrottledFrameRequestCallbackDocs.IsEmpty() ||
+         !mAutoFocusFlushDocuments.IsEmpty() || !mEarlyRunners.IsEmpty();
+}
+
+void nsRefreshDriver::AppendObserverDescriptionsToString(
+    nsACString& aStr) const {
+  for (const ObserverArray& array : mObservers) {
+    for (const auto& observer : array.EndLimitedRange()) {
+      aStr.AppendPrintf("%s [%s], ", observer.mDescription,
+                        kFlushTypeNames[observer.mFlushType]);
+    }
+  }
+  if (mViewManagerFlushIsPending && !mThrottled) {
+    aStr.AppendLiteral("View manager flush pending, ");
+  }
+  if (!mAnimationEventFlushObservers.IsEmpty()) {
+    aStr.AppendPrintf("%zux Animation event flush observer, ",
+                      mAnimationEventFlushObservers.Length());
+  }
+  if (!mResizeEventFlushObservers.IsEmpty()) {
+    aStr.AppendPrintf("%zux Resize event flush observer, ",
+                      mResizeEventFlushObservers.Length());
+  }
+  if (!mStyleFlushObservers.IsEmpty()) {
+    aStr.AppendPrintf("%zux Style flush observer, ",
+                      mStyleFlushObservers.Length());
+  }
+  if (!mLayoutFlushObservers.IsEmpty()) {
+    aStr.AppendPrintf("%zux Layout flush observer, ",
+                      mLayoutFlushObservers.Length());
+  }
+  if (!mPendingFullscreenEvents.IsEmpty()) {
+    aStr.AppendPrintf("%zux Pending fullscreen event, ",
+                      mPendingFullscreenEvents.Length());
+  }
+  if (!mFrameRequestCallbackDocs.IsEmpty()) {
+    aStr.AppendPrintf("%zux Frame request callback doc, ",
+                      mFrameRequestCallbackDocs.Length());
+  }
+  if (!mThrottledFrameRequestCallbackDocs.IsEmpty()) {
+    aStr.AppendPrintf("%zux Throttled frame request callback doc, ",
+                      mThrottledFrameRequestCallbackDocs.Length());
+  }
+  if (!mAutoFocusFlushDocuments.IsEmpty()) {
+    aStr.AppendPrintf("%zux AutoFocus flush doc, ",
+                      mAutoFocusFlushDocuments.Length());
+  }
+  if (!mEarlyRunners.IsEmpty()) {
+    aStr.AppendPrintf("%zux Early runner, ", mEarlyRunners.Length());
+  }
+  // Remove last ", "
+  aStr.Truncate(aStr.Length() - 2);
+}
+
+bool nsRefreshDriver::HasImageRequests() const {
+  for (const auto& data : mStartTable.Values()) {
+    if (!data->mEntries.IsEmpty()) {
+      return true;
+    }
+  }
+
+  return !mRequests.IsEmpty();
+}
+
+auto nsRefreshDriver::GetReasonsToTick() const -> TickReasons {
+  TickReasons reasons = TickReasons::eNone;
+  if (HasObservers()) {
+    reasons |= TickReasons::eHasObservers;
+  }
+  if (HasImageRequests() && !mThrottled) {
+    reasons |= TickReasons::eHasImageRequests;
+  }
+  if (mNeedToUpdateResizeObservers) {
+    reasons |= TickReasons::eNeedsToNotifyResizeObservers;
+  }
+  if (mNeedToUpdateIntersectionObservations) {
+    reasons |= TickReasons::eNeedsToUpdateIntersectionObservations;
+  }
+  if (mMightNeedMediaQueryListenerUpdate) {
+    reasons |= TickReasons::eHasPendingMediaQueryListeners;
+  }
+  if (mNeedToUpdateContentRelevancy) {
+    reasons |= TickReasons::eNeedsToUpdateContentRelevancy;
+  }
+  if (!mVisualViewportResizeEvents.IsEmpty()) {
+    reasons |= TickReasons::eHasVisualViewportResizeEvents;
+  }
+  if (!mScrollEvents.IsEmpty()) {
+    reasons |= TickReasons::eHasScrollEvents;
+  }
+  if (!mVisualViewportScrollEvents.IsEmpty()) {
+    reasons |= TickReasons::eHasVisualViewportScrollEvents;
+  }
+  if (mPresContext && mPresContext->IsRoot() &&
+      mPresContext->NeedsMoreTicksForUserInput()) {
+    reasons |= TickReasons::eRootNeedsMoreTicksForUserInput;
+  }
+  return reasons;
+}
+
+void nsRefreshDriver::AppendTickReasonsToString(TickReasons aReasons,
+                                                nsACString& aStr) const {
+  if (aReasons == TickReasons::eNone) {
+    aStr.AppendLiteral(" <none>");
+    return;
+  }
+
+  if (aReasons & TickReasons::eHasObservers) {
+    aStr.AppendLiteral(" HasObservers (");
+    AppendObserverDescriptionsToString(aStr);
+    aStr.AppendLiteral(")");
+  }
+  if (aReasons & TickReasons::eHasImageRequests) {
+    aStr.AppendLiteral(" HasImageAnimations");
+  }
+  if (aReasons & TickReasons::eNeedsToNotifyResizeObservers) {
+    aStr.AppendLiteral(" NeedsToNotifyResizeObservers");
+  }
+  if (aReasons & TickReasons::eNeedsToUpdateIntersectionObservations) {
+    aStr.AppendLiteral(" NeedsToUpdateIntersectionObservations");
+  }
+  if (aReasons & TickReasons::eHasPendingMediaQueryListeners) {
+    aStr.AppendLiteral(" HasPendingMediaQueryListeners");
+  }
+  if (aReasons & TickReasons::eNeedsToUpdateContentRelevancy) {
+    aStr.AppendLiteral(" NeedsToUpdateContentRelevancy");
+  }
+  if (aReasons & TickReasons::eHasVisualViewportResizeEvents) {
+    aStr.AppendLiteral(" HasVisualViewportResizeEvents");
+  }
+  if (aReasons & TickReasons::eHasScrollEvents) {
+    aStr.AppendLiteral(" HasScrollEvents");
+  }
+  if (aReasons & TickReasons::eHasVisualViewportScrollEvents) {
+    aStr.AppendLiteral(" HasVisualViewportScrollEvents");
+  }
+  if (aReasons & TickReasons::eRootNeedsMoreTicksForUserInput) {
+    aStr.AppendLiteral(" RootNeedsMoreTicksForUserInput");
+  }
+}
+
+bool nsRefreshDriver::
+    ShouldKeepTimerRunningWhileWaitingForFirstContentfulPaint() {
+  // On top level content pages keep the timer running initially so that we
+  // paint the page soon enough.
+  if (mThrottled || mTestControllingRefreshes || !XRE_IsContentProcess() ||
+      !mPresContext->Document()->IsTopLevelContentDocument() ||
+      mPresContext->Document()->IsInitialDocument() ||
+      gfxPlatform::IsInLayoutAsapMode() ||
+      mPresContext->HadFirstContentfulPaint() ||
+      mPresContext->Document()->GetReadyStateEnum() ==
+          Document::READYSTATE_COMPLETE) {
+    return false;
+  }
+  if (mBeforeFirstContentfulPaintTimerRunningLimit.IsNull()) {
+    // Don't let the timer to run forever, so limit to 4s for now.
+    mBeforeFirstContentfulPaintTimerRunningLimit =
+        TimeStamp::Now() + TimeDuration::FromSeconds(4.0f);
+  }
+
+  return TimeStamp::Now() <= mBeforeFirstContentfulPaintTimerRunningLimit;
+}
+
+bool nsRefreshDriver::ShouldKeepTimerRunningAfterPageLoad() {
+  if (mHasExceededAfterLoadTickPeriod ||
+      !StaticPrefs::layout_keep_ticking_after_load_ms() || mThrottled ||
+      mTestControllingRefreshes || !XRE_IsContentProcess() ||
+      !mPresContext->Document()->IsTopLevelContentDocument() ||
+      TaskController::Get()->PendingMainthreadTaskCountIncludingSuspended() ==
+          0 ||
+      gfxPlatform::IsInLayoutAsapMode()) {
+    // Make the next check faster.
+    mHasExceededAfterLoadTickPeriod = true;
+    return false;
+  }
+
+  nsPIDOMWindowInner* innerWindow = mPresContext->Document()->GetInnerWindow();
+  if (!innerWindow) {
+    return false;
+  }
+  auto* perf =
+      static_cast<PerformanceMainThread*>(innerWindow->GetPerformance());
+  if (!perf) {
+    return false;
+  }
+  nsDOMNavigationTiming* timing = perf->GetDOMTiming();
+  if (!timing) {
+    return false;
+  }
+  TimeStamp loadend = timing->LoadEventEnd();
+  if (!loadend) {
+    return false;
+  }
+  // Keep ticking after the page load for some time.
+  const bool retval =
+      (loadend + TimeDuration::FromMilliseconds(
+                     StaticPrefs::layout_keep_ticking_after_load_ms())) >
+      TimeStamp::Now();
+  if (!retval) {
+    mHasExceededAfterLoadTickPeriod = true;
+  }
+  return retval;
+}
+
+nsRefreshDriver::ObserverArray& nsRefreshDriver::ArrayFor(
+    FlushType aFlushType) {
+  switch (aFlushType) {
+    case FlushType::Event:
+      return mObservers[0];
+    case FlushType::Style:
+    case FlushType::Frames:
+      return mObservers[1];
+    case FlushType::Layout:
+      return mObservers[2];
+    case FlushType::Display:
+      return mObservers[3];
+    default:
+      MOZ_CRASH("We don't track refresh observers for this flush type");
+  }
+}
+
+/*
+ * nsITimerCallback implementation
+ */
+
+void nsRefreshDriver::DoTick() {
+  MOZ_ASSERT(!IsFrozen(), "Why are we notified while frozen?");
+  MOZ_ASSERT(mPresContext, "Why are we notified after disconnection?");
+  MOZ_ASSERT(!nsContentUtils::GetCurrentJSContext(),
+             "Shouldn't have a JSContext on the stack");
+
+  if (mTestControllingRefreshes) {
+    Tick(VsyncId(), mMostRecentRefresh);
+  } else {
+    Tick(VsyncId(), TimeStamp::Now());
+  }
+}
+
+struct DocumentFrameCallbacks {
+  explicit DocumentFrameCallbacks(Document* aDocument) : mDocument(aDocument) {}
+
+  RefPtr<Document> mDocument;
+  nsTArray<FrameRequest> mCallbacks;
+};
+
+static void TakeFrameRequestCallbacksFrom(
+    Document* aDocument, nsTArray<DocumentFrameCallbacks>& aTarget) {
+  aTarget.AppendElement(aDocument);
+  aDocument->TakeFrameRequestCallbacks(aTarget.LastElement().mCallbacks);
+}
+
+void nsRefreshDriver::ScheduleAutoFocusFlush(Document* aDocument) {
+  MOZ_ASSERT(!mAutoFocusFlushDocuments.Contains(aDocument));
+  mAutoFocusFlushDocuments.AppendElement(aDocument);
+  EnsureTimerStarted();
+}
+
+void nsRefreshDriver::FlushAutoFocusDocuments() {
+  nsTArray<RefPtr<Document>> docs(std::move(mAutoFocusFlushDocuments));
+
+  for (const auto& doc : docs) {
+    MOZ_KnownLive(doc)->FlushAutoFocusCandidates();
+  }
+}
+
+void nsRefreshDriver::MaybeIncreaseMeasuredTicksSinceLoading() {
+  if (mPresContext && mPresContext->IsRoot()) {
+    mPresContext->MaybeIncreaseMeasuredTicksSinceLoading();
+  }
+}
+
+void nsRefreshDriver::CancelFlushAutoFocus(Document* aDocument) {
+  mAutoFocusFlushDocuments.RemoveElement(aDocument);
+}
+
+// https://fullscreen.spec.whatwg.org/#run-the-fullscreen-steps
+void nsRefreshDriver::RunFullscreenSteps() {
+  // Swap out the current pending events
+  nsTArray<UniquePtr<PendingFullscreenEvent>> pendings(
+      std::move(mPendingFullscreenEvents));
+  for (UniquePtr<PendingFullscreenEvent>& event : pendings) {
+    event->Dispatch();
+  }
+}
+
+void nsRefreshDriver::UpdateIntersectionObservations(TimeStamp aNowTime) {
+  AUTO_PROFILER_LABEL_RELEVANT_FOR_JS("Compute intersections", LAYOUT);
+
+  AutoTArray<RefPtr<Document>, 32> documents;
+
+  if (mPresContext->Document()->HasIntersectionObservers()) {
+    documents.AppendElement(mPresContext->Document());
+  }
+
+  mPresContext->Document()->CollectDescendantDocuments(
+      documents, [](const Document* document) -> bool {
+        return document->HasIntersectionObservers();
+      });
+
+  for (const auto& doc : documents) {
+    doc->UpdateIntersectionObservations(aNowTime);
+    doc->ScheduleIntersectionObserverNotification();
+  }
+
+  mNeedToUpdateIntersectionObservations = false;
+}
+
+void nsRefreshDriver::UpdateRelevancyOfContentVisibilityAutoFrames() {
+  if (!mNeedToUpdateContentRelevancy) {
+    return;
+  }
+
+  if (RefPtr<PresShell> topLevelPresShell = mPresContext->GetPresShell()) {
+    topLevelPresShell->UpdateRelevancyOfContentVisibilityAutoFrames();
+  }
+
+  mPresContext->Document()->EnumerateSubDocuments([](Document& aSubDoc) {
+    if (PresShell* presShell = aSubDoc.GetPresShell()) {
+      presShell->UpdateRelevancyOfContentVisibilityAutoFrames();
+    }
+    return CallState::Continue;
+  });
+
+  mNeedToUpdateContentRelevancy = false;
+}
+
+void nsRefreshDriver::DetermineProximityToViewportAndNotifyResizeObservers() {
+  AUTO_PROFILER_LABEL_RELEVANT_FOR_JS("Update the rendering: step 14", LAYOUT);
+  // NotifyResizeObservers might re-schedule us for next tick.
+  mNeedToUpdateResizeObservers = false;
+
+  if (MOZ_UNLIKELY(!mPresContext)) {
+    return;
+  }
+
+  auto ShouldCollect = [](const Document* aDocument) {
+    PresShell* ps = aDocument->GetPresShell();
+    if (!ps || !ps->DidInitialize()) {
+      // If there's no shell or it didn't initialize, then we'll run this code
+      // when the pres shell does the initial reflow.
+      return false;
+    }
+    return ps->HasContentVisibilityAutoFrames() ||
+           aDocument->HasResizeObservers();
+  };
+
+  AutoTArray<RefPtr<Document>, 32> documents;
+  if (ShouldCollect(mPresContext->Document())) {
+    documents.AppendElement(mPresContext->Document());
+  }
+  mPresContext->Document()->CollectDescendantDocuments(documents,
+                                                       ShouldCollect);
+
+  for (const RefPtr<Document>& doc : documents) {
+    MOZ_KnownLive(doc)->DetermineProximityToViewportAndNotifyResizeObservers();
+  }
+}
+
+void nsRefreshDriver::DispatchAnimationEvents() {
+  if (!mPresContext) {
+    return;
+  }
+
+  // Hold all AnimationEventDispatcher in mAnimationEventFlushObservers as
+  // a RefPtr<> array since each AnimationEventDispatcher might be destroyed
+  // during processing the previous dispatcher.
+  AutoTArray<RefPtr<AnimationEventDispatcher>, 16> dispatchers;
+  dispatchers.AppendElements(mAnimationEventFlushObservers);
+  mAnimationEventFlushObservers.Clear();
+
+  for (auto& dispatcher : dispatchers) {
+    dispatcher->DispatchEvents();
+  }
+}
+
+void nsRefreshDriver::RunFrameRequestCallbacks(TimeStamp aNowTime) {
+  // Grab all of our frame request callbacks up front.
+  nsTArray<DocumentFrameCallbacks> frameRequestCallbacks(
+      mFrameRequestCallbackDocs.Length() +
+      mThrottledFrameRequestCallbackDocs.Length());
+
+  // First, grab throttled frame request callbacks.
+  {
+    nsTArray<Document*> docsToRemove;
+
+    // We always tick throttled frame requests if the entire refresh driver is
+    // throttled, because in that situation throttled frame requests tick at the
+    // same frequency as non-throttled frame requests.
+    bool tickThrottledFrameRequests = mThrottled;
+
+    if (!tickThrottledFrameRequests &&
+        aNowTime >= mNextThrottledFrameRequestTick) {
+      mNextThrottledFrameRequestTick =
+          aNowTime + mThrottledFrameRequestInterval;
+      tickThrottledFrameRequests = true;
+    }
+
+    for (Document* doc : mThrottledFrameRequestCallbackDocs) {
+      if (tickThrottledFrameRequests) {
+        // We're ticking throttled documents, so grab this document's requests.
+        // We don't bother appending to docsToRemove because we're going to
+        // clear mThrottledFrameRequestCallbackDocs anyway.
+        TakeFrameRequestCallbacksFrom(doc, frameRequestCallbacks);
+      } else if (!doc->ShouldThrottleFrameRequests()) {
+        // This document is no longer throttled, so grab its requests even
+        // though we're not ticking throttled frame requests right now. If
+        // this is the first unthrottled document with frame requests, we'll
+        // enter high precision mode the next time the callback is scheduled.
+        TakeFrameRequestCallbacksFrom(doc, frameRequestCallbacks);
+        docsToRemove.AppendElement(doc);
+      }
+    }
+
+    // Remove all the documents we're ticking from
+    // mThrottledFrameRequestCallbackDocs so they can be readded as needed.
+    if (tickThrottledFrameRequests) {
+      mThrottledFrameRequestCallbackDocs.Clear();
+    } else {
+      // XXX(seth): We're using this approach to avoid concurrent modification
+      // of mThrottledFrameRequestCallbackDocs. docsToRemove usually has either
+      // zero elements or a very small number, so this should be OK in practice.
+      for (Document* doc : docsToRemove) {
+        mThrottledFrameRequestCallbackDocs.RemoveElement(doc);
+      }
+    }
+  }
+
+  // Now grab unthrottled frame request callbacks.
+  for (Document* doc : mFrameRequestCallbackDocs) {
+    TakeFrameRequestCallbacksFrom(doc, frameRequestCallbacks);
+  }
+
+  // Reset mFrameRequestCallbackDocs so they can be readded as needed.
+  mFrameRequestCallbackDocs.Clear();
+
+  if (!frameRequestCallbacks.IsEmpty()) {
+    AUTO_PROFILER_TRACING_MARKER_DOCSHELL("Paint",
+                                          "requestAnimationFrame callbacks",
+                                          GRAPHICS, GetDocShell(mPresContext));
+    for (const DocumentFrameCallbacks& docCallbacks : frameRequestCallbacks) {
+      TimeStamp startTime = TimeStamp::Now();
+
+      // XXXbz Bug 863140: GetInnerWindow can return the outer
+      // window in some cases.
+      nsPIDOMWindowInner* innerWindow =
+          docCallbacks.mDocument->GetInnerWindow();
+      DOMHighResTimeStamp timeStamp = 0;
+      if (innerWindow) {
+        if (Performance* perf = innerWindow->GetPerformance()) {
+          timeStamp = perf->TimeStampToDOMHighResForRendering(aNowTime);
+        }
+        // else window is partially torn down already
+      }
+      for (auto& callback : docCallbacks.mCallbacks) {
+        if (docCallbacks.mDocument->IsCanceledFrameRequestCallback(
+                callback.mHandle)) {
+          continue;
+        }
+
+        nsCOMPtr<nsIGlobalObject> global(innerWindow ? innerWindow->AsGlobal()
+                                                     : nullptr);
+        CallbackDebuggerNotificationGuard guard(
+            global, DebuggerNotificationType::RequestAnimationFrameCallback);
+
+        // MOZ_KnownLive is OK, because the stack array frameRequestCallbacks
+        // keeps callback alive and the mCallback strong reference can't be
+        // mutated by the call.
+        LogFrameRequestCallback::Run run(callback.mCallback);
+        MOZ_KnownLive(callback.mCallback)->Call(timeStamp);
+      }
+
+      if (docCallbacks.mDocument->GetReadyStateEnum() ==
+          Document::READYSTATE_COMPLETE) {
+        glean::performance_responsiveness::req_anim_frame_callback
+            .AccumulateRawDuration(TimeStamp::Now() - startTime);
+      } else {
+        glean::performance_pageload::req_anim_frame_callback
+            .AccumulateRawDuration(TimeStamp::Now() - startTime);
+      }
+    }
+  }
+}
+
+static StaticAutoPtr<AutoTArray<RefPtr<Task>, 8>> sPendingIdleTasks;
+
+void nsRefreshDriver::DispatchIdleTaskAfterTickUnlessExists(Task* aTask) {
+  if (!sPendingIdleTasks) {
+    sPendingIdleTasks = new AutoTArray<RefPtr<Task>, 8>();
+  } else {
+    if (sPendingIdleTasks->Contains(aTask)) {
+      return;
+    }
+  }
+
+  sPendingIdleTasks->AppendElement(aTask);
+}
+
+void nsRefreshDriver::CancelIdleTask(Task* aTask) {
+  if (!sPendingIdleTasks) {
+    return;
+  }
+
+  sPendingIdleTasks->RemoveElement(aTask);
+
+  if (sPendingIdleTasks->IsEmpty()) {
+    sPendingIdleTasks = nullptr;
+  }
+}
+
+static CallState ReduceAnimations(Document& aDocument) {
+  if (nsPresContext* pc = aDocument.GetPresContext()) {
+    if (pc->EffectCompositor()->NeedsReducing()) {
+      pc->EffectCompositor()->ReduceAnimations();
+    }
+  }
+  aDocument.EnumerateSubDocuments(ReduceAnimations);
+  return CallState::Continue;
+}
+
+bool nsRefreshDriver::TickObserverArray(uint32_t aIdx, TimeStamp aNowTime) {
+  for (RefPtr<nsARefreshObserver> obs : mObservers[aIdx].EndLimitedRange()) {
+    obs->WillRefresh(aNowTime);
+
+    if (!mPresContext || !mPresContext->GetPresShell()) {
+      return false;
+    }
+  }
+
+  // Any animation timelines updated above may cause animations to queue
+  // Promise resolution microtasks. We shouldn't run these, however, until we
+  // have fully updated the animation state.
+  //
+  // As per the "update animations and send events" procedure[1], we should
+  // remove replaced animations and then run these microtasks before
+  // dispatching the corresponding animation events.
+  //
+  // [1]
+  // https://drafts.csswg.org/web-animations-1/#update-animations-and-send-events
+  if (aIdx == 1) {
+    // This is the FlushType::Style case.
+    {
+      nsAutoMicroTask mt;
+      ReduceAnimations(*mPresContext->Document());
+    }
+
+    // Check if running the microtask checkpoint caused the pres context to
+    // be destroyed.
+    if (!mPresContext || !mPresContext->GetPresShell()) {
+      return false;
+    }
+
+    FlushAutoFocusDocuments();
+    DispatchScrollEvents();
+    DispatchVisualViewportScrollEvents();
+    EvaluateMediaQueriesAndReportChanges();
+    DispatchAnimationEvents();
+    RunFullscreenSteps();
+    RunFrameRequestCallbacks(aNowTime);
+    MaybeIncreaseMeasuredTicksSinceLoading();
+
+    if (mPresContext && mPresContext->GetPresShell()) {
+      AutoTArray<PresShell*, 16> observers;
+      observers.AppendElements(mStyleFlushObservers);
+      for (uint32_t j = observers.Length();
+           j && mPresContext && mPresContext->GetPresShell(); --j) {
+        // Make sure to not process observers which might have been removed
+        // during previous iterations.
+        PresShell* rawPresShell = observers[j - 1];
+        if (!mStyleFlushObservers.RemoveElement(rawPresShell)) {
+          continue;
+        }
+
+        LogPresShellObserver::Run run(rawPresShell, this);
+
+        RefPtr<PresShell> presShell = rawPresShell;
+        presShell->mObservingStyleFlushes = false;
+        presShell->FlushPendingNotifications(
+            ChangesToFlush(FlushType::Style, false));
+        // Inform the FontFaceSet that we ticked, so that it can resolve its
+        // ready promise if it needs to (though it might still be waiting on
+        // a layout flush).
+        presShell->NotifyFontFaceSetOnRefresh();
+        mNeedToRecomputeVisibility = true;
+
+        // Record the telemetry for events that occurred between ticks.
+        presShell->PingPerTickTelemetry(FlushType::Style);
+      }
+    }
+  } else if (aIdx == 2) {
+    // This is the FlushType::Layout case.
+    AutoTArray<PresShell*, 16> observers;
+    observers.AppendElements(mLayoutFlushObservers);
+    for (uint32_t j = observers.Length();
+         j && mPresContext && mPresContext->GetPresShell(); --j) {
+      // Make sure to not process observers which might have been removed
+      // during previous iterations.
+      PresShell* rawPresShell = observers[j - 1];
+      if (!mLayoutFlushObservers.RemoveElement(rawPresShell)) {
+        continue;
+      }
+
+      LogPresShellObserver::Run run(rawPresShell, this);
+
+      RefPtr<PresShell> presShell = rawPresShell;
+      presShell->mObservingLayoutFlushes = false;
+      presShell->mWasLastReflowInterrupted = false;
+      const ChangesToFlush ctf(FlushType::InterruptibleLayout, false);
+      presShell->FlushPendingNotifications(ctf);
+      if (presShell->FixUpFocus()) {
+        presShell->FlushPendingNotifications(ctf);
+      }
+
+      // Inform the FontFaceSet that we ticked, so that it can resolve its
+      // ready promise if it needs to.
+      presShell->NotifyFontFaceSetOnRefresh();
+      mNeedToRecomputeVisibility = true;
+
+      // Record the telemetry for events that occurred between ticks.
+      presShell->PingPerTickTelemetry(FlushType::Layout);
+    }
+  }
+
+  // The pres context may be destroyed during we do the flushing.
+  if (!mPresContext || !mPresContext->GetPresShell()) {
+    return false;
+  }
+
+  return true;
+}
+
+void nsRefreshDriver::Tick(VsyncId aId, TimeStamp aNowTime,
+                           IsExtraTick aIsExtraTick /* = No */) {
+  MOZ_ASSERT(!nsContentUtils::GetCurrentJSContext(),
+             "Shouldn't have a JSContext on the stack");
+
+  // We're either frozen or we were disconnected (likely in the middle
+  // of a tick iteration).  Just do nothing here, since our
+  // prescontext went away.
+  if (IsFrozen() || !mPresContext) {
+    return;
+  }
+
+  // We can have a race condition where the vsync timestamp
+  // is before the most recent refresh due to a forced refresh.
+  // The underlying assumption is that the refresh driver tick can only
+  // go forward in time, not backwards. To prevent the refresh
+  // driver from going back in time, just skip this tick and
+  // wait until the next tick.
+  // If this is an 'extra' tick, then we expect it to be using the same
+  // vsync id and timestamp as the original tick, so also allow those.
+  if ((aNowTime <= mMostRecentRefresh) && !mTestControllingRefreshes &&
+      aIsExtraTick == IsExtraTick::No) {
+    return;
+  }
+  auto cleanupInExtraTick = MakeScopeExit([&] { mInNormalTick = false; });
+  mInNormalTick = aIsExtraTick != IsExtraTick::Yes;
+
+  bool isPresentingInVR = false;
+#if defined(MOZ_WIDGET_ANDROID)
+  isPresentingInVR = gfx::VRManagerChild::IsPresenting();
+#endif  // defined(MOZ_WIDGET_ANDROID)
+
+  if (!isPresentingInVR && IsWaitingForPaint(aNowTime)) {
+    // In immersive VR mode, we do not get notifications when frames are
+    // presented, so we do not wait for the compositor in that mode.
+
+    // We're currently suspended waiting for earlier Tick's to
+    // be completed (on the Compositor). Mark that we missed the paint
+    // and keep waiting.
+    PROFILER_MARKER_UNTYPED(
+        "RefreshDriverTick waiting for paint", GRAPHICS,
+        MarkerInnerWindowIdFromDocShell(GetDocShell(mPresContext)));
+    return;
+  }
+
+  const TimeStamp previousRefresh = mMostRecentRefresh;
+  mMostRecentRefresh = aNowTime;
+
+  if (mRootRefresh) {
+    mRootRefresh->RemoveRefreshObserver(this, FlushType::Style);
+    mRootRefresh = nullptr;
+  }
+  mSkippedPaints = false;
+
+  RefPtr<PresShell> presShell = mPresContext->GetPresShell();
+  if (!presShell) {
+    StopTimer();
+    return;
+  }
+
+  TickReasons tickReasons = GetReasonsToTick();
+  if (tickReasons == TickReasons::eNone) {
+    // We no longer have any observers.
+    // Discard composition payloads because there is no paint.
+    mCompositionPayloads.Clear();
+
+    // We don't want to stop the timer when observers are initially
+    // removed, because sometimes observers can be added and removed
+    // often depending on what other things are going on and in that
+    // situation we don't want to thrash our timer.  So instead we
+    // wait until we get a Notify() call when we have no observers
+    // before stopping the timer.
+    // On top level content pages keep the timer running initially so that we
+    // paint the page soon enough.
+    if (ShouldKeepTimerRunningWhileWaitingForFirstContentfulPaint()) {
+      PROFILER_MARKER(
+          "RefreshDriverTick waiting for first contentful paint", GRAPHICS,
+          MarkerInnerWindowIdFromDocShell(GetDocShell(mPresContext)), Tracing,
+          "Paint");
+    } else if (ShouldKeepTimerRunningAfterPageLoad()) {
+      PROFILER_MARKER(
+          "RefreshDriverTick after page load", GRAPHICS,
+          MarkerInnerWindowIdFromDocShell(GetDocShell(mPresContext)), Tracing,
+          "Paint");
+    } else {
+      StopTimer();
+    }
+    return;
+  }
+
+  if (StaticPrefs::layout_skip_ticks_while_page_suspended()) {
+    Document* doc = mPresContext->Document();
+    nsPIDOMWindowInner* win = doc ? doc->GetInnerWindow() : nullptr;
+    // Synchronous DOM operations mark the document being in such. Window's
+    // suspend can be used also by external code. So we check here them both
+    // in order to limit rAF skipping to only those synchronous DOM APIs which
+    // also suspend window.
+    if (win && win->IsSuspended() && doc->IsInSyncOperation()) {
+      return;
+    }
+  }
+
+  AUTO_PROFILER_LABEL_RELEVANT_FOR_JS("RefreshDriver tick", LAYOUT);
+
+  nsAutoCString profilerStr;
+  if (profiler_thread_is_being_profiled_for_markers()) {
+    profilerStr.AppendLiteral("Tick reasons:");
+    AppendTickReasonsToString(tickReasons, profilerStr);
+  }
+  AUTO_PROFILER_MARKER_TEXT(
+      "RefreshDriverTick", GRAPHICS,
+      MarkerOptions(
+          MarkerStack::TakeBacktrace(std::move(mRefreshTimerStartedCause)),
+          MarkerInnerWindowIdFromDocShell(GetDocShell(mPresContext))),
+      profilerStr);
+
+  mResizeSuppressed = false;
+
+  bool oldInRefresh = mInRefresh;
+  auto restoreInRefresh = MakeScopeExit([&] { mInRefresh = oldInRefresh; });
+  mInRefresh = true;
+
+  AutoRestore<TimeStamp> restoreTickStart(mTickStart);
+  mTickStart = TimeStamp::Now();
+  mTickVsyncId = aId;
+  mTickVsyncTime = aNowTime;
+
+  gfxPlatform::GetPlatform()->SchedulePaintIfDeviceReset();
+
+  FlushForceNotifyContentfulPaintPresContext();
+
+  AutoTArray<nsCOMPtr<nsIRunnable>, 16> earlyRunners = std::move(mEarlyRunners);
+  for (auto& runner : earlyRunners) {
+    runner->Run();
+    // Early runners might destroy this pres context.
+    if (!mPresContext || !mPresContext->GetPresShell()) {
+      StopTimer();
+      return;
+    }
+  }
+
+  // Resize events should be fired before layout flushes or
+  // calling animation frame callbacks.
+  AutoTArray<RefPtr<PresShell>, 16> observers;
+  observers.AppendElements(mResizeEventFlushObservers);
+  for (RefPtr<PresShell>& presShell : Reversed(observers)) {
+    if (!mPresContext || !mPresContext->GetPresShell()) {
+      StopTimer();
+      return;
+    }
+    // Make sure to not process observers which might have been removed
+    // during previous iterations.
+    if (!mResizeEventFlushObservers.RemoveElement(presShell)) {
+      continue;
+    }
+    // MOZ_KnownLive because 'observers' is guaranteed to
+    // keep it alive.
+    //
+    // Fixing https://bugzilla.mozilla.org/show_bug.cgi?id=1620312 on its own
+    // won't help here, because 'observers' is non-const and we have the
+    // Reversed() going on too...
+    MOZ_KnownLive(presShell)->FireResizeEvent();
+  }
+  DispatchVisualViewportResizeEvents();
+
+  /*
+   * The timer holds a reference to |this| while calling |Notify|.
+   * However, implementations of |WillRefresh| are permitted to destroy
+   * the pres context, which will cause our |mPresContext| to become
+   * null.  If this happens, TickObserverArray will tell us by returning
+   * false, and we must stop notifying observers.
+   */
+  // XXXdholbert This would be cleaner as a loop, but for now it's helpful to
+  // have these calls separated out, so that we can figure out which
+  // observer-category is involved from the backtrace of crash reports.
+  bool keepGoing = true;
+  MOZ_ASSERT(ArrayLength(mObservers) == 4,
+             "if this changes, then we need to add or remove calls to "
+             "TickObserverArray below");
+  keepGoing = keepGoing && TickObserverArray(0, aNowTime);
+  keepGoing = keepGoing && TickObserverArray(1, aNowTime);
+  keepGoing = keepGoing && TickObserverArray(2, aNowTime);
+  keepGoing = keepGoing && TickObserverArray(3, aNowTime);
+  if (!keepGoing) {
+    StopTimer();
+    return;
+  }
+
+  // Recompute approximate frame visibility if it's necessary and enough time
+  // has passed since the last time we did it.
+  if (mNeedToRecomputeVisibility && !mThrottled &&
+      aNowTime >= mNextRecomputeVisibilityTick &&
+      !presShell->IsPaintingSuppressed()) {
+    mNextRecomputeVisibilityTick = aNowTime + mMinRecomputeVisibilityInterval;
+    mNeedToRecomputeVisibility = false;
+
+    presShell->ScheduleApproximateFrameVisibilityUpdateNow();
+  }
+
+  // Update any popups that may need to be moved or hidden due to their
+  // anchor changing.
+  if (nsXULPopupManager* pm = nsXULPopupManager::GetInstance()) {
+    pm->UpdatePopupPositions(this);
+  }
+
+  // Update the relevancy of the content of any `content-visibility: auto`
+  // elements. The specification says: "Specifically, such changes will
+  // take effect between steps 13 and 14 of Update the Rendering step of
+  // the Processing Model (between “run the animation frame callbacks” and
+  // “run the update intersection observations steps”)."
+  // https://drafts.csswg.org/css-contain/#cv-notes
+  UpdateRelevancyOfContentVisibilityAutoFrames();
+
+  // Step 14 (https://html.spec.whatwg.org/#update-the-rendering).
+  // 1) Initial proximity to the viewport determination for
+  // content-visibility:auto elements and 2) Resize observers notifications.
+  DetermineProximityToViewportAndNotifyResizeObservers();
+  if (MOZ_UNLIKELY(!mPresContext || !mPresContext->GetPresShell())) {
+    // A resize observer callback apparently destroyed our PresContext.
+    StopTimer();
+    return;
+  }
+
+  UpdateIntersectionObservations(aNowTime);
+
+  UpdateAnimatedImages(previousRefresh, aNowTime);
+
+  bool dispatchTasksAfterTick = false;
+  if (mViewManagerFlushIsPending && !mThrottled) {
+    nsCString transactionId;
+    if (profiler_thread_is_being_profiled_for_markers()) {
+      transactionId.AppendLiteral("Transaction ID: ");
+      transactionId.AppendInt((uint64_t)mNextTransactionId);
+    }
+    AUTO_PROFILER_MARKER_TEXT(
+        "ViewManagerFlush", GRAPHICS,
+        MarkerOptions(
+            MarkerInnerWindowIdFromDocShell(GetDocShell(mPresContext)),
+            MarkerStack::TakeBacktrace(std::move(mViewManagerFlushCause))),
+        transactionId);
+
+    // Forward our composition payloads to the layer manager.
+    if (!mCompositionPayloads.IsEmpty()) {
+      nsCOMPtr<nsIWidget> widget = mPresContext->GetRootWidget();
+      WindowRenderer* renderer = widget ? widget->GetWindowRenderer() : nullptr;
+      if (renderer && renderer->AsWebRender()) {
+        renderer->AsWebRender()->RegisterPayloads(mCompositionPayloads);
+      }
+      mCompositionPayloads.Clear();
+    }
+
+#ifdef MOZ_DUMP_PAINTING
+    if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+      printf_stderr("Starting ProcessPendingUpdates\n");
+    }
+#endif
+
+    mViewManagerFlushIsPending = false;
+    RefPtr<nsViewManager> vm = mPresContext->GetPresShell()->GetViewManager();
+    const bool skipPaint = isPresentingInVR;
+    // Skip the paint in immersive VR mode because whatever we paint here will
+    // not end up on the screen. The screen is displaying WebGL content from a
+    // single canvas in that mode.
+    if (!skipPaint) {
+      PaintTelemetry::AutoRecordPaint record;
+      vm->ProcessPendingUpdates();
+    }
+
+#ifdef MOZ_DUMP_PAINTING
+    if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+      printf_stderr("Ending ProcessPendingUpdates\n");
+    }
+#endif
+
+    dispatchTasksAfterTick = true;
+    mHasScheduleFlush = false;
+  } else {
+    // No paint happened, discard composition payloads.
+    mCompositionPayloads.Clear();
+  }
+
+#ifndef ANDROID /* bug 1142079 */
+  double totalMs = (TimeStamp::Now() - mTickStart).ToMilliseconds();
+  mozilla::Telemetry::Accumulate(mozilla::Telemetry::REFRESH_DRIVER_TICK,
+                                 static_cast<uint32_t>(totalMs));
+#endif
+
+  if (mNotifyDOMContentFlushed) {
+    mNotifyDOMContentFlushed = false;
+    mPresContext->NotifyDOMContentFlushed();
+  }
+
+  for (nsAPostRefreshObserver* observer :
+       mPostRefreshObservers.ForwardRange()) {
+    observer->DidRefresh();
+  }
+
+  NS_ASSERTION(mInRefresh, "Still in refresh");
+
+  if (mPresContext->IsRoot() && XRE_IsContentProcess() &&
+      StaticPrefs::gfx_content_always_paint()) {
+    ScheduleViewManagerFlush();
+  }
+
+  if (dispatchTasksAfterTick && sPendingIdleTasks) {
+    UniquePtr<AutoTArray<RefPtr<Task>, 8>> tasks(sPendingIdleTasks.forget());
+    for (RefPtr<Task>& taskWithDelay : *tasks) {
+      TaskController::Get()->AddTask(taskWithDelay.forget());
+    }
+  }
+}
+
+void nsRefreshDriver::UpdateAnimatedImages(TimeStamp aPreviousRefresh,
+                                           TimeStamp aNowTime) {
+  if (mThrottled) {
+    // Don't do this when throttled, as the compositor might be paused and we
+    // don't want to queue a lot of paints, see bug 1828587.
+    return;
+  }
+  // Perform notification to imgIRequests subscribed to listen for refresh
+  // events.
+  for (const auto& entry : mStartTable) {
+    const uint32_t& delay = entry.GetKey();
+    ImageStartData* data = entry.GetWeak();
+
+    if (data->mEntries.IsEmpty()) {
+      continue;
+    }
+
+    if (data->mStartTime) {
+      TimeStamp& start = *data->mStartTime;
+
+      if (aPreviousRefresh >= start && aNowTime >= start) {
+        TimeDuration prev = aPreviousRefresh - start;
+        TimeDuration curr = aNowTime - start;
+        uint32_t prevMultiple = uint32_t(prev.ToMilliseconds()) / delay;
+
+        // We want to trigger images' refresh if we've just crossed over a
+        // multiple of the first image's start time. If so, set the animation
+        // start time to the nearest multiple of the delay and move all the
+        // images in this table to the main requests table.
+        if (prevMultiple != uint32_t(curr.ToMilliseconds()) / delay) {
+          mozilla::TimeStamp desired =
+              start + TimeDuration::FromMilliseconds(prevMultiple * delay);
+          BeginRefreshingImages(data->mEntries, desired);
+        }
+      } else {
+        // Sometimes the start time can be in the future if we spin a nested
+        // event loop and re-entrantly tick. In that case, setting the
+        // animation start time to the start time seems like the least bad
+        // thing we can do.
+        mozilla::TimeStamp desired = start;
+        BeginRefreshingImages(data->mEntries, desired);
+      }
+    } else {
+      // This is the very first time we've drawn images with this time delay.
+      // Set the animation start time to "now" and move all the images in this
+      // table to the main requests table.
+      mozilla::TimeStamp desired = aNowTime;
+      BeginRefreshingImages(data->mEntries, desired);
+      data->mStartTime.emplace(aNowTime);
+    }
+  }
+
+  if (!mRequests.IsEmpty()) {
+    // RequestRefresh may run scripts, so it's not safe to directly call it
+    // while using a hashtable enumerator to enumerate mRequests in case
+    // script modifies the hashtable. Instead, we build a (local) array of
+    // images to refresh, and then we refresh each image in that array.
+    nsTArray<nsCOMPtr<imgIContainer>> imagesToRefresh(mRequests.Count());
+
+    for (const auto& req : mRequests) {
+      nsCOMPtr<imgIContainer> image;
+      if (NS_SUCCEEDED(req->GetImage(getter_AddRefs(image)))) {
+        imagesToRefresh.AppendElement(image.forget());
+      }
+    }
+
+    for (const auto& image : imagesToRefresh) {
+      image->RequestRefresh(aNowTime);
+    }
+  }
+}
+
+void nsRefreshDriver::BeginRefreshingImages(RequestTable& aEntries,
+                                            mozilla::TimeStamp aDesired) {
+  for (const auto& req : aEntries) {
+    mRequests.Insert(req);
+
+    nsCOMPtr<imgIContainer> image;
+    if (NS_SUCCEEDED(req->GetImage(getter_AddRefs(image)))) {
+      image->SetAnimationStartTime(aDesired);
+    }
+  }
+  aEntries.Clear();
+}
+
+void nsRefreshDriver::Freeze() {
+  StopTimer();
+  mFreezeCount++;
+}
+
+void nsRefreshDriver::Thaw() {
+  NS_ASSERTION(mFreezeCount > 0, "Thaw() called on an unfrozen refresh driver");
+
+  if (mFreezeCount > 0) {
+    mFreezeCount--;
+  }
+
+  if (mFreezeCount == 0) {
+    if (HasObservers() || HasImageRequests()) {
+      // FIXME: This isn't quite right, since our EnsureTimerStarted call
+      // updates our mMostRecentRefresh, but the DoRefresh call won't run
+      // and notify our observers until we get back to the event loop.
+      // Thus MostRecentRefresh() will lie between now and the DoRefresh.
+      RefPtr<nsRunnableMethod<nsRefreshDriver>> event = NewRunnableMethod(
+          "nsRefreshDriver::DoRefresh", this, &nsRefreshDriver::DoRefresh);
+      nsPresContext* pc = GetPresContext();
+      if (pc) {
+        pc->Document()->Dispatch(event.forget());
+        EnsureTimerStarted();
+      } else {
+        NS_ERROR("Thawing while document is being destroyed");
+      }
+    }
+  }
+}
+
+void nsRefreshDriver::FinishedWaitingForTransaction() {
+  if (mSkippedPaints && !IsInRefresh() &&
+      (HasObservers() || HasImageRequests()) && CanDoCatchUpTick()) {
+    NS_DispatchToCurrentThreadQueue(
+        NS_NewRunnableFunction(
+            "nsRefreshDriver::FinishedWaitingForTransaction",
+            [self = RefPtr{this}]() {
+              if (self->CanDoCatchUpTick()) {
+                self->Tick(self->mActiveTimer->MostRecentRefreshVsyncId(),
+                           self->mActiveTimer->MostRecentRefresh());
+              }
+            }),
+        EventQueuePriority::Vsync);
+  }
+  mWaitingForTransaction = false;
+  mSkippedPaints = false;
+}
+
+mozilla::layers::TransactionId nsRefreshDriver::GetTransactionId(
+    bool aThrottle) {
+  mNextTransactionId = mNextTransactionId.Next();
+  LOG("[%p] Allocating transaction id %" PRIu64, this, mNextTransactionId.mId);
+
+  // If this a paint from within a normal tick, and the caller hasn't explicitly
+  // asked for it to skip being throttled, then record this transaction as
+  // pending and maybe disable painting until some transactions are processed.
+  if (aThrottle && mInNormalTick) {
+    mPendingTransactions.AppendElement(mNextTransactionId);
+    if (TooManyPendingTransactions() && !mWaitingForTransaction &&
+        !mTestControllingRefreshes) {
+      LOG("[%p] Hit max pending transaction limit, entering wait mode", this);
+      mWaitingForTransaction = true;
+      mSkippedPaints = false;
+    }
+  }
+
+  return mNextTransactionId;
+}
+
+mozilla::layers::TransactionId nsRefreshDriver::LastTransactionId() const {
+  return mNextTransactionId;
+}
+
+void nsRefreshDriver::RevokeTransactionId(
+    mozilla::layers::TransactionId aTransactionId) {
+  MOZ_ASSERT(aTransactionId == mNextTransactionId);
+  LOG("[%p] Revoking transaction id %" PRIu64, this, aTransactionId.mId);
+  if (AtPendingTransactionLimit() &&
+      mPendingTransactions.Contains(aTransactionId) && mWaitingForTransaction) {
+    LOG("[%p] No longer over pending transaction limit, leaving wait state",
+        this);
+    MOZ_ASSERT(!mSkippedPaints,
+               "How did we skip a paint when we're in the middle of one?");
+    FinishedWaitingForTransaction();
+  }
+
+  // Notify the pres context so that it can deliver MozAfterPaint for this
+  // id if any caller was expecting it.
+  nsPresContext* pc = GetPresContext();
+  if (pc) {
+    pc->NotifyRevokingDidPaint(aTransactionId);
+  }
+  // Remove aTransactionId from the set of outstanding transactions since we're
+  // no longer waiting on it to be completed, but don't revert
+  // mNextTransactionId since we can't use the id again.
+  mPendingTransactions.RemoveElement(aTransactionId);
+}
+
+void nsRefreshDriver::ClearPendingTransactions() {
+  LOG("[%p] ClearPendingTransactions", this);
+  mPendingTransactions.Clear();
+  mWaitingForTransaction = false;
+}
+
+void nsRefreshDriver::ResetInitialTransactionId(
+    mozilla::layers::TransactionId aTransactionId) {
+  mNextTransactionId = aTransactionId;
+}
+
+mozilla::TimeStamp nsRefreshDriver::GetTransactionStart() { return mTickStart; }
+
+VsyncId nsRefreshDriver::GetVsyncId() { return mTickVsyncId; }
+
+mozilla::TimeStamp nsRefreshDriver::GetVsyncStart() { return mTickVsyncTime; }
+
+void nsRefreshDriver::NotifyTransactionCompleted(
+    mozilla::layers::TransactionId aTransactionId) {
+  LOG("[%p] Completed transaction id %" PRIu64, this, aTransactionId.mId);
+  mPendingTransactions.RemoveElement(aTransactionId);
+  if (mWaitingForTransaction && !TooManyPendingTransactions()) {
+    LOG("[%p] No longer over pending transaction limit, leaving wait state",
+        this);
+    FinishedWaitingForTransaction();
+  }
+}
+
+void nsRefreshDriver::WillRefresh(mozilla::TimeStamp aTime) {
+  mRootRefresh->RemoveRefreshObserver(this, FlushType::Style);
+  mRootRefresh = nullptr;
+  if (mSkippedPaints) {
+    DoRefresh();
+  }
+}
+
+bool nsRefreshDriver::IsWaitingForPaint(mozilla::TimeStamp aTime) {
+  if (mTestControllingRefreshes) {
+    return false;
+  }
+
+  if (mWaitingForTransaction) {
+    LOG("[%p] Over max pending transaction limit when trying to paint, "
+        "skipping",
+        this);
+    mSkippedPaints = true;
+    return true;
+  }
+
+  // Try find the 'root' refresh driver for the current window and check
+  // if that is waiting for a paint.
+  nsPresContext* pc = GetPresContext();
+  nsPresContext* rootContext = pc ? pc->GetRootPresContext() : nullptr;
+  if (rootContext) {
+    nsRefreshDriver* rootRefresh = rootContext->RefreshDriver();
+    if (rootRefresh && rootRefresh != this) {
+      if (rootRefresh->IsWaitingForPaint(aTime)) {
+        if (mRootRefresh != rootRefresh) {
+          if (mRootRefresh) {
+            mRootRefresh->RemoveRefreshObserver(this, FlushType::Style);
+          }
+          rootRefresh->AddRefreshObserver(this, FlushType::Style,
+                                          "Waiting for paint");
+          mRootRefresh = rootRefresh;
+        }
+        mSkippedPaints = true;
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+void nsRefreshDriver::SetActivity(bool aIsActive) {
+  const bool shouldThrottle = !aIsActive;
+  if (mThrottled == shouldThrottle) {
+    return;
+  }
+  mThrottled = shouldThrottle;
+  if (mActiveTimer || GetReasonsToTick() != TickReasons::eNone) {
+    // We want to switch our timer type here, so just stop and restart the
+    // timer.
+    EnsureTimerStarted(eForceAdjustTimer);
+  }
+}
+
+nsPresContext* nsRefreshDriver::GetPresContext() const { return mPresContext; }
+
+void nsRefreshDriver::DoRefresh() {
+  // Don't do a refresh unless we're in a state where we should be refreshing.
+  if (!IsFrozen() && mPresContext && mActiveTimer) {
+    DoTick();
+  }
+}
+
+#ifdef DEBUG
+bool nsRefreshDriver::IsRefreshObserver(nsARefreshObserver* aObserver,
+                                        FlushType aFlushType) {
+  ObserverArray& array = ArrayFor(aFlushType);
+  return array.Contains(aObserver);
+}
+#endif
+
+void nsRefreshDriver::ScheduleViewManagerFlush() {
+  NS_ASSERTION(mPresContext && mPresContext->IsRoot(),
+               "Should only schedule view manager flush on root prescontexts");
+  mViewManagerFlushIsPending = true;
+  if (!mViewManagerFlushCause) {
+    mViewManagerFlushCause = profiler_capture_backtrace();
+  }
+  mHasScheduleFlush = true;
+  EnsureTimerStarted(eNeverAdjustTimer);
+}
+
+void nsRefreshDriver::ScheduleFrameRequestCallbacks(Document* aDocument) {
+  NS_ASSERTION(mFrameRequestCallbackDocs.IndexOf(aDocument) ==
+                       mFrameRequestCallbackDocs.NoIndex &&
+                   mThrottledFrameRequestCallbackDocs.IndexOf(aDocument) ==
+                       mThrottledFrameRequestCallbackDocs.NoIndex,
+               "Don't schedule the same document multiple times");
+  if (aDocument->ShouldThrottleFrameRequests()) {
+    mThrottledFrameRequestCallbackDocs.AppendElement(aDocument);
+  } else {
+    mFrameRequestCallbackDocs.AppendElement(aDocument);
+  }
+
+  // make sure that the timer is running
+  EnsureTimerStarted();
+}
+
+void nsRefreshDriver::RevokeFrameRequestCallbacks(Document* aDocument) {
+  mFrameRequestCallbackDocs.RemoveElement(aDocument);
+  mThrottledFrameRequestCallbackDocs.RemoveElement(aDocument);
+  // No need to worry about restarting our timer in slack mode if it's already
+  // running; that will happen automatically when it fires.
+}
+
+void nsRefreshDriver::ScheduleFullscreenEvent(
+    UniquePtr<PendingFullscreenEvent> aEvent) {
+  mPendingFullscreenEvents.AppendElement(std::move(aEvent));
+  // make sure that the timer is running
+  EnsureTimerStarted();
+}
+
+void nsRefreshDriver::CancelPendingFullscreenEvents(Document* aDocument) {
+  for (auto i : Reversed(IntegerRange(mPendingFullscreenEvents.Length()))) {
+    if (mPendingFullscreenEvents[i]->Document() == aDocument) {
+      mPendingFullscreenEvents.RemoveElementAt(i);
+    }
+  }
+}
+
+void nsRefreshDriver::CancelPendingAnimationEvents(
+    AnimationEventDispatcher* aDispatcher) {
+  MOZ_ASSERT(aDispatcher);
+  aDispatcher->ClearEventQueue();
+  mAnimationEventFlushObservers.RemoveElement(aDispatcher);
+}
+
+/* static */
+TimeStamp nsRefreshDriver::GetIdleDeadlineHint(TimeStamp aDefault,
+                                               IdleCheck aCheckType) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!aDefault.IsNull());
+
+  // For computing idleness of refresh drivers we only care about
+  // sRegularRateTimerList, since we consider refresh drivers attached to
+  // sThrottledRateTimer to be inactive. This implies that tasks
+  // resulting from a tick on the sRegularRateTimer counts as being
+  // busy but tasks resulting from a tick on sThrottledRateTimer
+  // counts as being idle.
+  if (sRegularRateTimer) {
+    TimeStamp retVal = sRegularRateTimer->GetIdleDeadlineHint(aDefault);
+    if (retVal != aDefault) {
+      return retVal;
+    }
+  }
+
+  TimeStamp hint = TimeStamp();
+  if (sRegularRateTimerList) {
+    for (RefreshDriverTimer* timer : *sRegularRateTimerList) {
+      TimeStamp newHint = timer->GetIdleDeadlineHint(aDefault);
+      if (newHint < aDefault && (hint.IsNull() || newHint < hint)) {
+        hint = newHint;
+      }
+    }
+  }
+
+  if (!hint.IsNull()) {
+    return hint;
+  }
+
+  if (aCheckType == IdleCheck::AllVsyncListeners && XRE_IsParentProcess()) {
+    Maybe<TimeDuration> maybeRate =
+        mozilla::gfx::VsyncSource::GetFastestVsyncRate();
+    if (maybeRate.isSome()) {
+      TimeDuration minIdlePeriod =
+          TimeDuration::FromMilliseconds(StaticPrefs::idle_period_min());
+      TimeDuration layoutIdleLimit = TimeDuration::FromMilliseconds(
+          StaticPrefs::layout_idle_period_time_limit());
+      TimeDuration rate = *maybeRate - layoutIdleLimit;
+
+      // If the rate is very short, don't let it affect idle processing in the
+      // parent process too much.
+      rate = std::max(rate, minIdlePeriod + minIdlePeriod);
+
+      TimeStamp newHint = TimeStamp::Now() + rate;
+      if (newHint < aDefault) {
+        return newHint;
+      }
+    }
+  }
+
+  return aDefault;
+}
+
+/* static */
+Maybe<TimeStamp> nsRefreshDriver::GetNextTickHint() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (sRegularRateTimer) {
+    return sRegularRateTimer->GetNextTickHint();
+  }
+
+  Maybe<TimeStamp> hint = Nothing();
+  if (sRegularRateTimerList) {
+    for (RefreshDriverTimer* timer : *sRegularRateTimerList) {
+      if (Maybe<TimeStamp> newHint = timer->GetNextTickHint()) {
+        if (!hint || newHint.value() < hint.value()) {
+          hint = newHint;
+        }
+      }
+    }
+  }
+  return hint;
+}
+
+/* static */
+bool nsRefreshDriver::IsRegularRateTimerTicking() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (sRegularRateTimer) {
+    if (sRegularRateTimer->IsTicking()) {
+      return true;
+    }
+  }
+
+  if (sRegularRateTimerList) {
+    for (RefreshDriverTimer* timer : *sRegularRateTimerList) {
+      if (timer->IsTicking()) {
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+void nsRefreshDriver::Disconnect() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  StopTimer();
+
+  mEarlyRunners.Clear();
+
+  if (mPresContext) {
+    mPresContext = nullptr;
+    if (--sRefreshDriverCount == 0) {
+      Shutdown();
+    }
+  }
+}
+
+#undef LOG