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diff --git a/accessible/base/NotificationController.h b/accessible/base/NotificationController.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#ifndef mozilla_a11y_NotificationController_h_
+#define mozilla_a11y_NotificationController_h_
+
+#include "EventQueue.h"
+
+#include "nsClassHashtable.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsIFrame.h"
+#include "nsRefreshObservers.h"
+#include "nsTHashSet.h"
+
+#include <utility>
+
+#ifdef A11Y_LOG
+#  include "Logging.h"
+#endif
+
+namespace mozilla {
+
+class PresShell;
+
+namespace a11y {
+
+class DocAccessible;
+
+/**
+ * Notification interface.
+ */
+class Notification {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(mozilla::a11y::Notification)
+
+  /**
+   * Process notification.
+   */
+  virtual void Process() = 0;
+
+ protected:
+  Notification() {}
+
+  /**
+   * Protected destructor, to discourage deletion outside of Release():
+   */
+  virtual ~Notification() {}
+
+ private:
+  Notification(const Notification&);
+  Notification& operator=(const Notification&);
+};
+
+/**
+ * Template class for generic notification.
+ *
+ * @note  Instance is kept as a weak ref, the caller must guarantee it exists
+ *        longer than the document accessible owning the notification controller
+ *        that this notification is processed by.
+ */
+template <class Class, class... Args>
+class TNotification : public Notification {
+ public:
+  typedef void (Class::*Callback)(Args*...);
+
+  TNotification(Class* aInstance, Callback aCallback, Args*... aArgs)
+      : mInstance(aInstance), mCallback(aCallback), mArgs(aArgs...) {}
+  virtual ~TNotification() { mInstance = nullptr; }
+
+  virtual void Process() override {
+    ProcessHelper(std::index_sequence_for<Args...>{});
+  }
+
+ private:
+  TNotification(const TNotification&);
+  TNotification& operator=(const TNotification&);
+
+  template <size_t... Indices>
+  void ProcessHelper(std::index_sequence<Indices...>) {
+    (mInstance->*mCallback)(std::get<Indices>(mArgs)...);
+  }
+
+  Class* mInstance;
+  Callback mCallback;
+  std::tuple<RefPtr<Args>...> mArgs;
+};
+
+/**
+ * Used to process notifications from core for the document accessible.
+ */
+class NotificationController final : public EventQueue,
+                                     public nsARefreshObserver {
+ public:
+  NotificationController(DocAccessible* aDocument, PresShell* aPresShell);
+
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void) override;
+  NS_IMETHOD_(MozExternalRefCountType) Release(void) override;
+
+  NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS(NotificationController)
+
+  /**
+   * Shutdown the notification controller.
+   */
+  void Shutdown();
+
+  /**
+   * Add an accessible event into the queue to process it later.
+   */
+  void QueueEvent(AccEvent* aEvent) {
+    if (PushEvent(aEvent)) {
+      ScheduleProcessing();
+    }
+  }
+
+  /**
+   * Queue a mutation event to emit if not coalesced away.  Returns true if the
+   * event was queued and has not yet been coalesced.
+   */
+  bool QueueMutationEvent(AccTreeMutationEvent* aEvent);
+
+  /**
+   * Coalesce all queued mutation events.
+   */
+  void CoalesceMutationEvents();
+
+  /**
+   * Schedule binding the child document to the tree of this document.
+   */
+  void ScheduleChildDocBinding(DocAccessible* aDocument);
+
+  /**
+   * Schedule the accessible tree update because of rendered text changes.
+   */
+  inline void ScheduleTextUpdate(nsIContent* aTextNode) {
+    // Make sure we are not called with a node that is not in the DOM tree or
+    // not visible.
+    MOZ_ASSERT(aTextNode->GetParentNode(), "A text node is not in DOM");
+    MOZ_ASSERT(aTextNode->GetPrimaryFrame(),
+               "A text node doesn't have a frame");
+    MOZ_ASSERT(aTextNode->GetPrimaryFrame()->StyleVisibility()->IsVisible(),
+               "A text node is not visible");
+
+    mTextArray.AppendElement(aTextNode);
+
+    ScheduleProcessing();
+  }
+
+  /**
+   * Pend accessible tree update for content insertion.
+   */
+  void ScheduleContentInsertion(LocalAccessible* aContainer,
+                                nsTArray<nsCOMPtr<nsIContent>>& aInsertions);
+
+  /**
+   * Pend an accessible subtree relocation.
+   */
+  void ScheduleRelocation(LocalAccessible* aOwner) {
+    if (!mRelocations.Contains(aOwner)) {
+      // XXX(Bug 1631371) Check if this should use a fallible operation as it
+      // pretended earlier, or change the return type to void.
+      mRelocations.AppendElement(aOwner);
+      ScheduleProcessing();
+    }
+  }
+
+  /**
+   * Start to observe refresh to make notifications and events processing after
+   * layout.
+   */
+  void ScheduleProcessing();
+
+  /**
+   * Process the generic notification synchronously if there are no pending
+   * layout changes and no notifications are pending or being processed right
+   * now. Otherwise, queue it up to process asynchronously.
+   *
+   * @note  The caller must guarantee that the given instance still exists when
+   *        the notification is processed.
+   */
+  template <class Class, class... Args>
+  inline void HandleNotification(
+      Class* aInstance,
+      typename TNotification<Class, Args...>::Callback aMethod,
+      Args*... aArgs) {
+    if (!IsUpdatePending()) {
+#ifdef A11Y_LOG
+      if (mozilla::a11y::logging::IsEnabled(
+              mozilla::a11y::logging::eNotifications)) {
+        mozilla::a11y::logging::Text("sync notification processing");
+      }
+#endif
+      (aInstance->*aMethod)(aArgs...);
+      return;
+    }
+
+    RefPtr<Notification> notification =
+        new TNotification<Class, Args...>(aInstance, aMethod, aArgs...);
+    if (notification) {
+      // XXX(Bug 1631371) Check if this should use a fallible operation as it
+      // pretended earlier.
+      mNotifications.AppendElement(notification);
+      ScheduleProcessing();
+    }
+  }
+
+  /**
+   * Schedule the generic notification to process asynchronously.
+   *
+   * @note  The caller must guarantee that the given instance still exists when
+   *        the notification is processed.
+   */
+  template <class Class>
+  inline void ScheduleNotification(
+      Class* aInstance, typename TNotification<Class>::Callback aMethod) {
+    RefPtr<Notification> notification =
+        new TNotification<Class>(aInstance, aMethod);
+    if (notification) {
+      // XXX(Bug 1631371) Check if this should use a fallible operation as it
+      // pretended earlier.
+      mNotifications.AppendElement(notification);
+      ScheduleProcessing();
+    }
+  }
+
+  template <class Class, class Arg>
+  inline void ScheduleNotification(
+      Class* aInstance, typename TNotification<Class, Arg>::Callback aMethod,
+      Arg* aArg) {
+    RefPtr<Notification> notification =
+        new TNotification<Class, Arg>(aInstance, aMethod, aArg);
+    if (notification) {
+      // XXX(Bug 1631371) Check if this should use a fallible operation as it
+      // pretended earlier.
+      mNotifications.AppendElement(notification);
+      ScheduleProcessing();
+    }
+  }
+
+#ifdef DEBUG
+  bool IsUpdating() const {
+    return mObservingState == eRefreshProcessingForUpdate;
+  }
+#endif
+
+ protected:
+  virtual ~NotificationController();
+
+  nsCycleCollectingAutoRefCnt mRefCnt;
+  NS_DECL_OWNINGTHREAD
+
+  /**
+   * Return true if the accessible tree state update is pending.
+   */
+  bool IsUpdatePending();
+
+  /**
+   * Return true if we should wait for processing from the parent before we can
+   * process our own queue.
+   */
+  bool WaitingForParent();
+
+ private:
+  NotificationController(const NotificationController&);
+  NotificationController& operator=(const NotificationController&);
+
+  // nsARefreshObserver
+  virtual void WillRefresh(mozilla::TimeStamp aTime) override;
+
+ private:
+  /**
+   * Remove a specific hide event if it should not be propagated.
+   */
+  void CoalesceHideEvent(AccHideEvent* aHideEvent);
+
+  /**
+   * get rid of a mutation event that is no longer necessary.
+   */
+  void DropMutationEvent(AccTreeMutationEvent* aEvent);
+
+  /**
+   * Fire all necessary mutation events.
+   */
+  void ProcessMutationEvents();
+
+  /**
+   * Indicates whether we're waiting on an event queue processing from our
+   * notification controller to flush events.
+   */
+  enum eObservingState {
+    eNotObservingRefresh,
+    eRefreshObserving,
+    eRefreshProcessing,
+    eRefreshProcessingForUpdate
+  };
+  eObservingState mObservingState;
+
+  /**
+   * The presshell of the document accessible.
+   */
+  PresShell* mPresShell;
+
+  /**
+   * Child documents that needs to be bound to the tree.
+   */
+  nsTArray<RefPtr<DocAccessible>> mHangingChildDocuments;
+
+  /**
+   * Pending accessible tree update notifications for content insertions.
+   */
+  nsClassHashtable<nsRefPtrHashKey<LocalAccessible>,
+                   nsTArray<nsCOMPtr<nsIContent>>>
+      mContentInsertions;
+
+  template <class T>
+  class nsCOMPtrHashKey : public PLDHashEntryHdr {
+   public:
+    typedef T* KeyType;
+    typedef const T* KeyTypePointer;
+
+    explicit nsCOMPtrHashKey(const T* aKey) : mKey(const_cast<T*>(aKey)) {}
+    nsCOMPtrHashKey(nsCOMPtrHashKey<T>&& aOther)
+        : PLDHashEntryHdr(std::move(aOther)), mKey(std::move(aOther.mKey)) {}
+    ~nsCOMPtrHashKey() {}
+
+    KeyType GetKey() const { return mKey; }
+    bool KeyEquals(KeyTypePointer aKey) const { return aKey == mKey; }
+
+    static KeyTypePointer KeyToPointer(KeyType aKey) { return aKey; }
+    static PLDHashNumber HashKey(KeyTypePointer aKey) {
+      return NS_PTR_TO_INT32(aKey) >> 2;
+    }
+
+    enum { ALLOW_MEMMOVE = true };
+
+   protected:
+    nsCOMPtr<T> mKey;
+  };
+
+  /**
+   * Pending accessible tree update notifications for rendered text changes.
+   * When there are a lot of nearby text insertions (e.g. during a reflow), it
+   * is much more performant to process them in order because we then benefit
+   * from the layout line cursor. Therefore, we use an array here.
+   */
+  nsTArray<nsCOMPtr<nsIContent>> mTextArray;
+
+  /**
+   * Other notifications like DOM events. Don't make this an AutoTArray; we
+   * use SwapElements() on it.
+   */
+  nsTArray<RefPtr<Notification>> mNotifications;
+
+  /**
+   * Holds all scheduled relocations.
+   */
+  nsTArray<RefPtr<LocalAccessible>> mRelocations;
+
+  /**
+   * A list of all mutation events we may want to emit.  Ordered from the first
+   * event that should be emitted to the last one to emit.
+   */
+  RefPtr<AccTreeMutationEvent> mFirstMutationEvent;
+  RefPtr<AccTreeMutationEvent> mLastMutationEvent;
+
+  /**
+   * A class to map an accessible and event type to an event.
+   */
+  class EventMap {
+   public:
+    enum EventType {
+      ShowEvent = 0x0,
+      HideEvent = 0x1,
+      ReorderEvent = 0x2,
+    };
+
+    void PutEvent(AccTreeMutationEvent* aEvent);
+    AccTreeMutationEvent* GetEvent(LocalAccessible* aTarget, EventType aType);
+    void RemoveEvent(AccTreeMutationEvent* aEvent);
+    void Clear() { mTable.Clear(); }
+
+   private:
+    EventType GetEventType(AccTreeMutationEvent* aEvent);
+
+    nsRefPtrHashtable<nsUint64HashKey, AccTreeMutationEvent> mTable;
+  };
+
+  EventMap mMutationMap;
+  uint32_t mEventGeneration;
+};
+
+}  // namespace a11y
+}  // namespace mozilla
+
+#endif  // mozilla_a11y_NotificationController_h_