Adding upstream version 86.0.1.upstream/86.0.1upstream

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

1 files changed, 1977 insertions, 0 deletions

diff --git a/docshell/shistory/nsSHistory.cpp b/docshell/shistory/nsSHistory.cpp
new file mode 100644
index 0000000000..1581cd55c2
--- /dev/null
+++ b/docshell/shistory/nsSHistory.cpp
@@ -0,0 +1,1977 @@
+/* -*- 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/. */
+
+#include "nsSHistory.h"
+
+#include <algorithm>
+
+#include "nsContentUtils.h"
+#include "nsCOMArray.h"
+#include "nsComponentManagerUtils.h"
+#include "nsDocShell.h"
+#include "nsIContentViewer.h"
+#include "nsIDocShell.h"
+#include "nsDocShellLoadState.h"
+#include "nsIDocShellTreeItem.h"
+#include "nsILayoutHistoryState.h"
+#include "nsIObserverService.h"
+#include "nsISHEntry.h"
+#include "nsISHistoryListener.h"
+#include "nsIURI.h"
+#include "nsIXULRuntime.h"
+#include "nsNetUtil.h"
+#include "nsSHEntry.h"
+#include "SessionHistoryEntry.h"
+#include "nsTArray.h"
+#include "prsystem.h"
+
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/CanonicalBrowsingContext.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/LinkedList.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/dom/CanonicalBrowsingContext.h"
+#include "nsIWebNavigation.h"
+#include "nsDocShellLoadTypes.h"
+#include "base/process.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+#define PREF_SHISTORY_SIZE "browser.sessionhistory.max_entries"
+#define PREF_SHISTORY_MAX_TOTAL_VIEWERS \
+  "browser.sessionhistory.max_total_viewers"
+#define CONTENT_VIEWER_TIMEOUT_SECONDS \
+  "browser.sessionhistory.contentViewerTimeout"
+
+// Default this to time out unused content viewers after 30 minutes
+#define CONTENT_VIEWER_TIMEOUT_SECONDS_DEFAULT (30 * 60)
+
+static const char* kObservedPrefs[] = {
+    PREF_SHISTORY_SIZE, PREF_SHISTORY_MAX_TOTAL_VIEWERS, nullptr};
+
+static int32_t gHistoryMaxSize = 50;
+// List of all SHistory objects, used for content viewer cache eviction
+static LinkedList<nsSHistory> gSHistoryList;
+// Max viewers allowed total, across all SHistory objects - negative default
+// means we will calculate how many viewers to cache based on total memory
+int32_t nsSHistory::sHistoryMaxTotalViewers = -1;
+
+// A counter that is used to be able to know the order in which
+// entries were touched, so that we can evict older entries first.
+static uint32_t gTouchCounter = 0;
+
+extern mozilla::LazyLogModule gSHLog;
+
+LazyLogModule gSHistoryLog("nsSHistory");
+
+#define LOG(format) MOZ_LOG(gSHistoryLog, mozilla::LogLevel::Debug, format)
+
+extern mozilla::LazyLogModule gPageCacheLog;
+
+// This macro makes it easier to print a log message which includes a URI's
+// spec.  Example use:
+//
+//  nsIURI *uri = [...];
+//  LOG_SPEC(("The URI is %s.", _spec), uri);
+//
+#define LOG_SPEC(format, uri)                        \
+  PR_BEGIN_MACRO                                     \
+  if (MOZ_LOG_TEST(gSHistoryLog, LogLevel::Debug)) { \
+    nsAutoCString _specStr("(null)"_ns);             \
+    if (uri) {                                       \
+      _specStr = uri->GetSpecOrDefault();            \
+    }                                                \
+    const char* _spec = _specStr.get();              \
+    LOG(format);                                     \
+  }                                                  \
+  PR_END_MACRO
+
+// This macro makes it easy to log a message including an SHEntry's URI.
+// For example:
+//
+//  nsCOMPtr<nsISHEntry> shentry = [...];
+//  LOG_SHENTRY_SPEC(("shentry %p has uri %s.", shentry.get(), _spec), shentry);
+//
+#define LOG_SHENTRY_SPEC(format, shentry)            \
+  PR_BEGIN_MACRO                                     \
+  if (MOZ_LOG_TEST(gSHistoryLog, LogLevel::Debug)) { \
+    nsCOMPtr<nsIURI> uri = shentry->GetURI();        \
+    LOG_SPEC(format, uri);                           \
+  }                                                  \
+  PR_END_MACRO
+
+// Iterates over all registered session history listeners.
+#define ITERATE_LISTENERS(body)                                           \
+  PR_BEGIN_MACRO {                                                        \
+    for (const nsWeakPtr& weakPtr : mListeners.EndLimitedRange()) {       \
+      nsCOMPtr<nsISHistoryListener> listener = do_QueryReferent(weakPtr); \
+      if (listener) {                                                     \
+        body                                                              \
+      }                                                                   \
+    }                                                                     \
+  }                                                                       \
+  PR_END_MACRO
+
+// Calls a given method on all registered session history listeners.
+#define NOTIFY_LISTENERS(method, args) \
+  ITERATE_LISTENERS(listener->method args;);
+
+// Calls a given method on all registered session history listeners.
+// Listeners may return 'false' to cancel an action so make sure that we
+// set the return value to 'false' if one of the listeners wants to cancel.
+#define NOTIFY_LISTENERS_CANCELABLE(method, retval, args) \
+  PR_BEGIN_MACRO {                                        \
+    bool canceled = false;                                \
+    retval = true;                                        \
+    ITERATE_LISTENERS(listener->method args;              \
+                      if (!retval) { canceled = true; }); \
+    if (canceled) {                                       \
+      retval = false;                                     \
+    }                                                     \
+  }                                                       \
+  PR_END_MACRO
+
+class MOZ_STACK_CLASS SHistoryChangeNotifier {
+ public:
+  explicit SHistoryChangeNotifier(nsSHistory* aHistory) {
+    // If we're already in an update, the outermost change notifier will
+    // update browsing context in the destructor.
+    if (!aHistory->HasOngoingUpdate()) {
+      aHistory->SetHasOngoingUpdate(true);
+      mSHistory = aHistory;
+      mInitialIndex = aHistory->Index();
+      mInitialLength = aHistory->Length();
+    }
+  }
+
+  ~SHistoryChangeNotifier() {
+    if (mSHistory) {
+      MOZ_ASSERT(mSHistory->HasOngoingUpdate());
+      mSHistory->SetHasOngoingUpdate(false);
+      if (mSHistory->GetBrowsingContext()) {
+        mSHistory->GetBrowsingContext()->SessionHistoryChanged(
+            mSHistory->Index() - mInitialIndex,
+            mSHistory->Length() - mInitialLength);
+      }
+
+      if (mozilla::SessionHistoryInParent() &&
+          mSHistory->GetBrowsingContext()) {
+        mSHistory->GetBrowsingContext()
+            ->Canonical()
+            ->HistoryCommitIndexAndLength();
+      }
+    }
+  }
+
+  RefPtr<nsSHistory> mSHistory;
+  int32_t mInitialIndex;
+  int32_t mInitialLength;
+};
+
+enum HistCmd { HIST_CMD_GOTOINDEX, HIST_CMD_RELOAD };
+
+class nsSHistoryObserver final : public nsIObserver {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  nsSHistoryObserver() {}
+
+  static void PrefChanged(const char* aPref, void* aSelf);
+  void PrefChanged(const char* aPref);
+
+ protected:
+  ~nsSHistoryObserver() {}
+};
+
+StaticRefPtr<nsSHistoryObserver> gObserver;
+
+NS_IMPL_ISUPPORTS(nsSHistoryObserver, nsIObserver)
+
+// static
+void nsSHistoryObserver::PrefChanged(const char* aPref, void* aSelf) {
+  static_cast<nsSHistoryObserver*>(aSelf)->PrefChanged(aPref);
+}
+
+void nsSHistoryObserver::PrefChanged(const char* aPref) {
+  nsSHistory::UpdatePrefs();
+  nsSHistory::GloballyEvictContentViewers();
+}
+
+NS_IMETHODIMP
+nsSHistoryObserver::Observe(nsISupports* aSubject, const char* aTopic,
+                            const char16_t* aData) {
+  if (!strcmp(aTopic, "cacheservice:empty-cache") ||
+      !strcmp(aTopic, "memory-pressure")) {
+    nsSHistory::GloballyEvictAllContentViewers();
+  }
+
+  return NS_OK;
+}
+
+void nsSHistory::EvictContentViewerForEntry(nsISHEntry* aEntry) {
+  nsCOMPtr<nsIContentViewer> viewer = aEntry->GetContentViewer();
+  if (viewer) {
+    LOG_SHENTRY_SPEC(("Evicting content viewer 0x%p for "
+                      "owning SHEntry 0x%p at %s.",
+                      viewer.get(), aEntry, _spec),
+                     aEntry);
+
+    // Drop the presentation state before destroying the viewer, so that
+    // document teardown is able to correctly persist the state.
+    NotifyListenersContentViewerEvicted(1);
+    aEntry->SetContentViewer(nullptr);
+    aEntry->SyncPresentationState();
+    viewer->Destroy();
+  }
+
+  // When dropping bfcache, we have to remove associated dynamic entries as
+  // well.
+  int32_t index = GetIndexOfEntry(aEntry);
+  if (index != -1) {
+    RemoveDynEntries(index, aEntry);
+  }
+}
+
+nsSHistory::nsSHistory(BrowsingContext* aRootBC)
+    : mRootBC(aRootBC),
+      mHasOngoingUpdate(false),
+      mIsRemote(false),
+      mIndex(-1),
+      mRequestedIndex(-1),
+      mRootDocShellID(aRootBC->GetHistoryID()) {
+  static bool sCalledStartup = false;
+  if (!sCalledStartup) {
+    Startup();
+    sCalledStartup = true;
+  }
+
+  // Add this new SHistory object to the list
+  gSHistoryList.insertBack(this);
+
+  // Init mHistoryTracker on setting mRootBC so we can bind its event
+  // target to the tabGroup.
+  nsPIDOMWindowOuter* win;
+  if (mRootBC && (win = mRootBC->GetDOMWindow())) {
+    nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(win);
+    mHistoryTracker = mozilla::MakeUnique<HistoryTracker>(
+        this,
+        mozilla::Preferences::GetUint(CONTENT_VIEWER_TIMEOUT_SECONDS,
+                                      CONTENT_VIEWER_TIMEOUT_SECONDS_DEFAULT),
+        global->EventTargetFor(mozilla::TaskCategory::Other));
+  }
+}
+
+nsSHistory::~nsSHistory() {}
+
+NS_IMPL_ADDREF(nsSHistory)
+NS_IMPL_RELEASE(nsSHistory)
+
+NS_INTERFACE_MAP_BEGIN(nsSHistory)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsISHistory)
+  NS_INTERFACE_MAP_ENTRY(nsISHistory)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+NS_INTERFACE_MAP_END
+
+// static
+uint32_t nsSHistory::CalcMaxTotalViewers() {
+// This value allows tweaking how fast the allowed amount of content viewers
+// grows with increasing amounts of memory. Larger values mean slower growth.
+#ifdef ANDROID
+#  define MAX_TOTAL_VIEWERS_BIAS 15.9
+#else
+#  define MAX_TOTAL_VIEWERS_BIAS 14
+#endif
+
+  // Calculate an estimate of how many ContentViewers we should cache based
+  // on RAM.  This assumes that the average ContentViewer is 4MB (conservative)
+  // and caps the max at 8 ContentViewers
+  //
+  // TODO: Should we split the cache memory betw. ContentViewer caching and
+  // nsCacheService?
+  //
+  // RAM    | ContentViewers | on Android
+  // -------------------------------------
+  // 32   Mb       0                0
+  // 64   Mb       1                0
+  // 128  Mb       2                0
+  // 256  Mb       3                1
+  // 512  Mb       5                2
+  // 768  Mb       6                2
+  // 1024 Mb       8                3
+  // 2048 Mb       8                5
+  // 3072 Mb       8                7
+  // 4096 Mb       8                8
+  uint64_t bytes = PR_GetPhysicalMemorySize();
+
+  if (bytes == 0) {
+    return 0;
+  }
+
+  // Conversion from unsigned int64_t to double doesn't work on all platforms.
+  // We need to truncate the value at INT64_MAX to make sure we don't
+  // overflow.
+  if (bytes > INT64_MAX) {
+    bytes = INT64_MAX;
+  }
+
+  double kBytesD = (double)(bytes >> 10);
+
+  // This is essentially the same calculation as for nsCacheService,
+  // except that we divide the final memory calculation by 4, since
+  // we assume each ContentViewer takes on average 4MB
+  uint32_t viewers = 0;
+  double x = std::log(kBytesD) / std::log(2.0) - MAX_TOTAL_VIEWERS_BIAS;
+  if (x > 0) {
+    viewers = (uint32_t)(x * x - x + 2.001);  // add .001 for rounding
+    viewers /= 4;
+  }
+
+  // Cap it off at 8 max
+  if (viewers > 8) {
+    viewers = 8;
+  }
+  return viewers;
+}
+
+// static
+void nsSHistory::UpdatePrefs() {
+  Preferences::GetInt(PREF_SHISTORY_SIZE, &gHistoryMaxSize);
+  if (mozilla::SessionHistoryInParent()) {
+    sHistoryMaxTotalViewers = 0;
+    return;
+  }
+
+  Preferences::GetInt(PREF_SHISTORY_MAX_TOTAL_VIEWERS,
+                      &sHistoryMaxTotalViewers);
+  // If the pref is negative, that means we calculate how many viewers
+  // we think we should cache, based on total memory
+  if (sHistoryMaxTotalViewers < 0) {
+    sHistoryMaxTotalViewers = CalcMaxTotalViewers();
+  }
+}
+
+// static
+nsresult nsSHistory::Startup() {
+  UpdatePrefs();
+
+  // The goal of this is to unbreak users who have inadvertently set their
+  // session history size to less than the default value.
+  int32_t defaultHistoryMaxSize =
+      Preferences::GetInt(PREF_SHISTORY_SIZE, 50, PrefValueKind::Default);
+  if (gHistoryMaxSize < defaultHistoryMaxSize) {
+    gHistoryMaxSize = defaultHistoryMaxSize;
+  }
+
+  // Allow the user to override the max total number of cached viewers,
+  // but keep the per SHistory cached viewer limit constant
+  if (!gObserver) {
+    gObserver = new nsSHistoryObserver();
+    Preferences::RegisterCallbacks(nsSHistoryObserver::PrefChanged,
+                                   kObservedPrefs, gObserver.get());
+
+    nsCOMPtr<nsIObserverService> obsSvc =
+        mozilla::services::GetObserverService();
+    if (obsSvc) {
+      // Observe empty-cache notifications so tahat clearing the disk/memory
+      // cache will also evict all content viewers.
+      obsSvc->AddObserver(gObserver, "cacheservice:empty-cache", false);
+
+      // Same for memory-pressure notifications
+      obsSvc->AddObserver(gObserver, "memory-pressure", false);
+    }
+  }
+
+  return NS_OK;
+}
+
+// static
+void nsSHistory::Shutdown() {
+  if (gObserver) {
+    Preferences::UnregisterCallbacks(nsSHistoryObserver::PrefChanged,
+                                     kObservedPrefs, gObserver.get());
+
+    nsCOMPtr<nsIObserverService> obsSvc =
+        mozilla::services::GetObserverService();
+    if (obsSvc) {
+      obsSvc->RemoveObserver(gObserver, "cacheservice:empty-cache");
+      obsSvc->RemoveObserver(gObserver, "memory-pressure");
+    }
+    gObserver = nullptr;
+  }
+}
+
+// static
+already_AddRefed<nsISHEntry> nsSHistory::GetRootSHEntry(nsISHEntry* aEntry) {
+  nsCOMPtr<nsISHEntry> rootEntry = aEntry;
+  nsCOMPtr<nsISHEntry> result = nullptr;
+  while (rootEntry) {
+    result = rootEntry;
+    rootEntry = result->GetParent();
+  }
+
+  return result.forget();
+}
+
+// static
+nsresult nsSHistory::WalkHistoryEntries(nsISHEntry* aRootEntry,
+                                        BrowsingContext* aBC,
+                                        WalkHistoryEntriesFunc aCallback,
+                                        void* aData) {
+  NS_ENSURE_TRUE(aRootEntry, NS_ERROR_FAILURE);
+
+  int32_t childCount = aRootEntry->GetChildCount();
+  for (int32_t i = 0; i < childCount; i++) {
+    nsCOMPtr<nsISHEntry> childEntry;
+    aRootEntry->GetChildAt(i, getter_AddRefs(childEntry));
+    if (!childEntry) {
+      // childEntry can be null for valid reasons, for example if the
+      // docshell at index i never loaded anything useful.
+      // Remember to clone also nulls in the child array (bug 464064).
+      aCallback(nullptr, nullptr, i, aData);
+      continue;
+    }
+
+    BrowsingContext* childBC = nullptr;
+    if (aBC) {
+      for (BrowsingContext* child : aBC->Children()) {
+        // If the SH pref is on and we are in the parent process, update
+        // canonical BC directly
+        bool foundChild = false;
+        if (mozilla::SessionHistoryInParent() && XRE_IsParentProcess()) {
+          if (child->Canonical()->HasHistoryEntry(childEntry)) {
+            childBC = child;
+            foundChild = true;
+          }
+        }
+
+        nsDocShell* docshell = static_cast<nsDocShell*>(child->GetDocShell());
+        if (docshell && docshell->HasHistoryEntry(childEntry)) {
+          childBC = docshell->GetBrowsingContext();
+          foundChild = true;
+        }
+
+        // XXX Simplify this once the old and new session history
+        // implementations don't run at the same time.
+        if (foundChild) {
+          break;
+        }
+      }
+    }
+
+    nsresult rv = aCallback(childEntry, childBC, i, aData);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  return NS_OK;
+}
+
+// callback data for WalkHistoryEntries
+struct MOZ_STACK_CLASS CloneAndReplaceData {
+  CloneAndReplaceData(uint32_t aCloneID, nsISHEntry* aReplaceEntry,
+                      bool aCloneChildren, nsISHEntry* aDestTreeParent)
+      : cloneID(aCloneID),
+        cloneChildren(aCloneChildren),
+        replaceEntry(aReplaceEntry),
+        destTreeParent(aDestTreeParent) {}
+
+  uint32_t cloneID;
+  bool cloneChildren;
+  nsISHEntry* replaceEntry;
+  nsISHEntry* destTreeParent;
+  nsCOMPtr<nsISHEntry> resultEntry;
+};
+
+nsresult nsSHistory::CloneAndReplaceChild(nsISHEntry* aEntry,
+                                          BrowsingContext* aOwnerBC,
+                                          int32_t aChildIndex, void* aData) {
+  nsCOMPtr<nsISHEntry> dest;
+
+  CloneAndReplaceData* data = static_cast<CloneAndReplaceData*>(aData);
+  uint32_t cloneID = data->cloneID;
+  nsISHEntry* replaceEntry = data->replaceEntry;
+
+  if (!aEntry) {
+    if (data->destTreeParent) {
+      data->destTreeParent->AddChild(nullptr, aChildIndex);
+    }
+    return NS_OK;
+  }
+
+  uint32_t srcID = aEntry->GetID();
+
+  nsresult rv = NS_OK;
+  if (srcID == cloneID) {
+    // Replace the entry
+    dest = replaceEntry;
+  } else {
+    // Clone the SHEntry...
+    rv = aEntry->Clone(getter_AddRefs(dest));
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  dest->SetIsSubFrame(true);
+
+  if (srcID != cloneID || data->cloneChildren) {
+    // Walk the children
+    CloneAndReplaceData childData(cloneID, replaceEntry, data->cloneChildren,
+                                  dest);
+    rv = nsSHistory::WalkHistoryEntries(aEntry, aOwnerBC, CloneAndReplaceChild,
+                                        &childData);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  if (srcID != cloneID && aOwnerBC) {
+    nsSHistory::HandleEntriesToSwapInDocShell(aOwnerBC, aEntry, dest);
+  }
+
+  if (data->destTreeParent) {
+    data->destTreeParent->AddChild(dest, aChildIndex);
+  }
+  data->resultEntry = dest;
+  return rv;
+}
+
+// static
+nsresult nsSHistory::CloneAndReplace(
+    nsISHEntry* aSrcEntry, BrowsingContext* aOwnerBC, uint32_t aCloneID,
+    nsISHEntry* aReplaceEntry, bool aCloneChildren, nsISHEntry** aDestEntry) {
+  NS_ENSURE_ARG_POINTER(aDestEntry);
+  NS_ENSURE_TRUE(aReplaceEntry, NS_ERROR_FAILURE);
+  CloneAndReplaceData data(aCloneID, aReplaceEntry, aCloneChildren, nullptr);
+  nsresult rv = CloneAndReplaceChild(aSrcEntry, aOwnerBC, 0, &data);
+  data.resultEntry.swap(*aDestEntry);
+  return rv;
+}
+
+// static
+void nsSHistory::WalkContiguousEntries(
+    nsISHEntry* aEntry, const std::function<void(nsISHEntry*)>& aCallback) {
+  MOZ_ASSERT(aEntry);
+
+  nsCOMPtr<nsISHistory> shistory = aEntry->GetShistory();
+  if (!shistory) {
+    // If there is no session history in the entry, it means this is not a root
+    // entry. So, we can return from here.
+    return;
+  }
+
+  int32_t index = shistory->GetIndexOfEntry(aEntry);
+  int32_t count = shistory->GetCount();
+
+  nsCOMPtr<nsIURI> targetURI = aEntry->GetURI();
+
+  // First, call the callback on the input entry.
+  aCallback(aEntry);
+
+  // Walk backward to find the entries that have the same origin as the
+  // input entry.
+  for (int32_t i = index - 1; i >= 0; i--) {
+    RefPtr<nsISHEntry> entry;
+    shistory->GetEntryAtIndex(i, getter_AddRefs(entry));
+    if (entry) {
+      nsCOMPtr<nsIURI> uri = entry->GetURI();
+      if (NS_FAILED(nsContentUtils::GetSecurityManager()->CheckSameOriginURI(
+              targetURI, uri, false, false))) {
+        break;
+      }
+
+      aCallback(entry);
+    }
+  }
+
+  // Then, Walk forward.
+  for (int32_t i = index + 1; i < count; i++) {
+    RefPtr<nsISHEntry> entry;
+    shistory->GetEntryAtIndex(i, getter_AddRefs(entry));
+    if (entry) {
+      nsCOMPtr<nsIURI> uri = entry->GetURI();
+      if (NS_FAILED(nsContentUtils::GetSecurityManager()->CheckSameOriginURI(
+              targetURI, uri, false, false))) {
+        break;
+      }
+
+      aCallback(entry);
+    }
+  }
+}
+
+NS_IMETHODIMP
+nsSHistory::AddChildSHEntryHelper(nsISHEntry* aCloneRef, nsISHEntry* aNewEntry,
+                                  BrowsingContext* aRootBC,
+                                  bool aCloneChildren) {
+  MOZ_ASSERT(aRootBC->IsTop());
+
+  /* You are currently in the rootDocShell.
+   * You will get here when a subframe has a new url
+   * to load and you have walked up the tree all the
+   * way to the top to clone the current SHEntry hierarchy
+   * and replace the subframe where a new url was loaded with
+   * a new entry.
+   */
+  nsCOMPtr<nsISHEntry> child;
+  nsCOMPtr<nsISHEntry> currentHE;
+  int32_t index = mIndex;
+  if (index < 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  GetEntryAtIndex(index, getter_AddRefs(currentHE));
+  NS_ENSURE_TRUE(currentHE, NS_ERROR_FAILURE);
+
+  nsresult rv = NS_OK;
+  uint32_t cloneID = aCloneRef->GetID();
+  rv = nsSHistory::CloneAndReplace(currentHE, aRootBC, cloneID, aNewEntry,
+                                   aCloneChildren, getter_AddRefs(child));
+
+  if (NS_SUCCEEDED(rv)) {
+    rv = AddEntry(child, true);
+    if (NS_SUCCEEDED(rv)) {
+      child->SetDocshellID(aRootBC->GetHistoryID());
+    }
+  }
+
+  return rv;
+}
+
+nsresult nsSHistory::SetChildHistoryEntry(nsISHEntry* aEntry,
+                                          BrowsingContext* aBC,
+                                          int32_t aEntryIndex, void* aData) {
+  SwapEntriesData* data = static_cast<SwapEntriesData*>(aData);
+  if (!aBC || aBC == data->ignoreBC) {
+    return NS_OK;
+  }
+
+  nsISHEntry* destTreeRoot = data->destTreeRoot;
+
+  nsCOMPtr<nsISHEntry> destEntry;
+
+  if (data->destTreeParent) {
+    // aEntry is a clone of some child of destTreeParent, but since the
+    // trees aren't necessarily in sync, we'll have to locate it.
+    // Note that we could set aShell's entry to null if we don't find a
+    // corresponding entry under destTreeParent.
+
+    uint32_t targetID = aEntry->GetID();
+
+    // First look at the given index, since this is the common case.
+    nsCOMPtr<nsISHEntry> entry;
+    data->destTreeParent->GetChildAt(aEntryIndex, getter_AddRefs(entry));
+    if (entry && entry->GetID() == targetID) {
+      destEntry.swap(entry);
+    } else {
+      int32_t childCount;
+      data->destTreeParent->GetChildCount(&childCount);
+      for (int32_t i = 0; i < childCount; ++i) {
+        data->destTreeParent->GetChildAt(i, getter_AddRefs(entry));
+        if (!entry) {
+          continue;
+        }
+
+        if (entry->GetID() == targetID) {
+          destEntry.swap(entry);
+          break;
+        }
+      }
+    }
+  } else {
+    destEntry = destTreeRoot;
+  }
+
+  nsSHistory::HandleEntriesToSwapInDocShell(aBC, aEntry, destEntry);
+  // Now handle the children of aEntry.
+  SwapEntriesData childData = {data->ignoreBC, destTreeRoot, destEntry};
+  return nsSHistory::WalkHistoryEntries(aEntry, aBC, SetChildHistoryEntry,
+                                        &childData);
+}
+
+// static
+void nsSHistory::HandleEntriesToSwapInDocShell(
+    mozilla::dom::BrowsingContext* aBC, nsISHEntry* aOldEntry,
+    nsISHEntry* aNewEntry) {
+  bool shPref = mozilla::SessionHistoryInParent();
+  if (aBC->IsInProcess() || !shPref) {
+    nsDocShell* docshell = static_cast<nsDocShell*>(aBC->GetDocShell());
+    if (docshell) {
+      docshell->SwapHistoryEntries(aOldEntry, aNewEntry);
+    }
+  } else {
+    // FIXME Bug 1633988: Need to update entries?
+  }
+
+  // XXX Simplify this once the old and new session history implementations
+  // don't run at the same time.
+  if (shPref && XRE_IsParentProcess()) {
+    aBC->Canonical()->SwapHistoryEntries(aOldEntry, aNewEntry);
+  }
+}
+
+void nsSHistory::UpdateRootBrowsingContextState() {
+  if (mRootBC) {
+    bool sameDocument = IsEmptyOrHasEntriesForSingleTopLevelPage();
+    if (sameDocument != mRootBC->GetIsSingleToplevelInHistory()) {
+      // If the browsing context is discarded then its session history is
+      // invalid and will go away.
+      Unused << mRootBC->SetIsSingleToplevelInHistory(sameDocument);
+    }
+  }
+}
+
+NS_IMETHODIMP
+nsSHistory::AddToRootSessionHistory(bool aCloneChildren, nsISHEntry* aOSHE,
+                                    BrowsingContext* aRootBC,
+                                    nsISHEntry* aEntry, uint32_t aLoadType,
+                                    bool aShouldPersist,
+                                    Maybe<int32_t>* aPreviousEntryIndex,
+                                    Maybe<int32_t>* aLoadedEntryIndex) {
+  MOZ_ASSERT(aRootBC->IsTop());
+
+  nsresult rv = NS_OK;
+
+  // If we need to clone our children onto the new session
+  // history entry, do so now.
+  if (aCloneChildren && aOSHE) {
+    uint32_t cloneID = aOSHE->GetID();
+    nsCOMPtr<nsISHEntry> newEntry;
+    nsSHistory::CloneAndReplace(aOSHE, aRootBC, cloneID, aEntry, true,
+                                getter_AddRefs(newEntry));
+    NS_ASSERTION(aEntry == newEntry,
+                 "The new session history should be in the new entry");
+  }
+  // This is the root docshell
+  bool addToSHistory = !LOAD_TYPE_HAS_FLAGS(
+      aLoadType, nsIWebNavigation::LOAD_FLAGS_REPLACE_HISTORY);
+  if (!addToSHistory) {
+    // Replace current entry in session history; If the requested index is
+    // valid, it indicates the loading was triggered by a history load, and
+    // we should replace the entry at requested index instead.
+    int32_t index = GetIndexForReplace();
+
+    // Replace the current entry with the new entry
+    if (index >= 0) {
+      rv = ReplaceEntry(index, aEntry);
+    } else {
+      // If we're trying to replace an inexistant shistory entry, append.
+      addToSHistory = true;
+    }
+  }
+  if (addToSHistory) {
+    // Add to session history
+    *aPreviousEntryIndex = Some(mIndex);
+    rv = AddEntry(aEntry, aShouldPersist);
+    *aLoadedEntryIndex = Some(mIndex);
+    MOZ_LOG(gPageCacheLog, LogLevel::Verbose,
+            ("Previous index: %d, Loaded index: %d",
+             aPreviousEntryIndex->value(), aLoadedEntryIndex->value()));
+  }
+  if (NS_SUCCEEDED(rv)) {
+    aEntry->SetDocshellID(aRootBC->GetHistoryID());
+  }
+  return rv;
+}
+
+/* Add an entry to the History list at mIndex and
+ * increment the index to point to the new entry
+ */
+NS_IMETHODIMP
+nsSHistory::AddEntry(nsISHEntry* aSHEntry, bool aPersist) {
+  NS_ENSURE_ARG(aSHEntry);
+
+  nsCOMPtr<nsISHistory> shistoryOfEntry = aSHEntry->GetShistory();
+  if (shistoryOfEntry && shistoryOfEntry != this) {
+    NS_WARNING(
+        "The entry has been associated to another nsISHistory instance. "
+        "Try nsISHEntry.clone() and nsISHEntry.abandonBFCacheEntry() "
+        "first if you're copying an entry from another nsISHistory.");
+    return NS_ERROR_FAILURE;
+  }
+
+  aSHEntry->SetShistory(this);
+
+  // If we have a root docshell, update the docshell id of the root shentry to
+  // match the id of that docshell
+  if (mRootBC) {
+    aSHEntry->SetDocshellID(mRootDocShellID);
+  }
+
+  if (mIndex >= 0) {
+    MOZ_ASSERT(mIndex < Length(), "Index out of range!");
+    if (mIndex >= Length()) {
+      return NS_ERROR_FAILURE;
+    }
+
+    if (mEntries[mIndex] && !mEntries[mIndex]->GetPersist()) {
+      NOTIFY_LISTENERS(OnHistoryReplaceEntry, ());
+      aSHEntry->SetPersist(aPersist);
+      mEntries[mIndex] = aSHEntry;
+      UpdateRootBrowsingContextState();
+      return NS_OK;
+    }
+  }
+  SHistoryChangeNotifier change(this);
+
+  nsCOMPtr<nsIURI> uri = aSHEntry->GetURI();
+  NOTIFY_LISTENERS(OnHistoryNewEntry, (uri, mIndex));
+
+  // Remove all entries after the current one, add the new one, and set the
+  // new one as the current one.
+  MOZ_ASSERT(mIndex >= -1);
+  aSHEntry->SetPersist(aPersist);
+  mEntries.TruncateLength(mIndex + 1);
+  mEntries.AppendElement(aSHEntry);
+  mIndex++;
+
+  // Purge History list if it is too long
+  if (gHistoryMaxSize >= 0 && Length() > gHistoryMaxSize) {
+    PurgeHistory(Length() - gHistoryMaxSize);
+  }
+
+  UpdateRootBrowsingContextState();
+
+  return NS_OK;
+}
+
+void nsSHistory::NotifyOnHistoryReplaceEntry() {
+  NOTIFY_LISTENERS(OnHistoryReplaceEntry, ());
+}
+
+/* Get size of the history list */
+NS_IMETHODIMP
+nsSHistory::GetCount(int32_t* aResult) {
+  MOZ_ASSERT(aResult, "null out param?");
+  *aResult = Length();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetIndex(int32_t* aResult) {
+  MOZ_ASSERT(aResult, "null out param?");
+  *aResult = mIndex;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::SetIndex(int32_t aIndex) {
+  if (aIndex < 0 || aIndex >= Length()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mIndex = aIndex;
+  return NS_OK;
+}
+
+/* Get the requestedIndex */
+NS_IMETHODIMP
+nsSHistory::GetRequestedIndex(int32_t* aResult) {
+  MOZ_ASSERT(aResult, "null out param?");
+  *aResult = mRequestedIndex;
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(void)
+nsSHistory::InternalSetRequestedIndex(int32_t aRequestedIndex) {
+  MOZ_ASSERT(aRequestedIndex >= -1 && aRequestedIndex < Length());
+  mRequestedIndex = aRequestedIndex;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetEntryAtIndex(int32_t aIndex, nsISHEntry** aResult) {
+  NS_ENSURE_ARG_POINTER(aResult);
+
+  if (aIndex < 0 || aIndex >= Length()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aResult = mEntries[aIndex];
+  NS_ADDREF(*aResult);
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(int32_t)
+nsSHistory::GetIndexOfEntry(nsISHEntry* aSHEntry) {
+  for (int32_t i = 0; i < Length(); i++) {
+    if (aSHEntry == mEntries[i]) {
+      return i;
+    }
+  }
+
+  return -1;
+}
+
+static void LogEntry(nsISHEntry* aEntry, int32_t aIndex, int32_t aTotal,
+                     const nsCString& aPrefix, bool aIsCurrent) {
+  if (!aEntry) {
+    MOZ_LOG(gSHLog, LogLevel::Debug,
+            (" %s+- %i SH Entry null\n", aPrefix.get(), aIndex));
+    return;
+  }
+
+  nsCOMPtr<nsIURI> uri = aEntry->GetURI();
+  nsAutoString title;
+  aEntry->GetTitle(title);
+
+  SHEntrySharedParentState* shared;
+  if (mozilla::SessionHistoryInParent()) {
+    shared = static_cast<SessionHistoryEntry*>(aEntry)->SharedInfo();
+  } else {
+    shared = static_cast<nsSHEntry*>(aEntry)->GetState();
+  }
+
+  nsID docShellId;
+  aEntry->GetDocshellID(docShellId);
+
+  int32_t childCount = aEntry->GetChildCount();
+
+  MOZ_LOG(gSHLog, LogLevel::Debug,
+          ("%s%s+- %i SH Entry %p %" PRIu64 " %s\n", aIsCurrent ? ">" : " ",
+           aPrefix.get(), aIndex, aEntry, shared->GetId(),
+           nsIDToCString(docShellId).get()));
+
+  nsCString prefix(aPrefix);
+  if (aIndex < aTotal - 1) {
+    prefix.AppendLiteral("|   ");
+  } else {
+    prefix.AppendLiteral("    ");
+  }
+
+  MOZ_LOG(gSHLog, LogLevel::Debug,
+          (" %s%s  URL = %s\n", prefix.get(), childCount > 0 ? "|" : " ",
+           uri->GetSpecOrDefault().get()));
+  MOZ_LOG(gSHLog, LogLevel::Debug,
+          (" %s%s  Title = %s\n", prefix.get(), childCount > 0 ? "|" : " ",
+           NS_LossyConvertUTF16toASCII(title).get()));
+
+  nsCOMPtr<nsISHEntry> prevChild;
+  for (int32_t i = 0; i < childCount; ++i) {
+    nsCOMPtr<nsISHEntry> child;
+    aEntry->GetChildAt(i, getter_AddRefs(child));
+    LogEntry(child, i, childCount, prefix, false);
+    child.swap(prevChild);
+  }
+}
+
+void nsSHistory::LogHistory() {
+  if (!MOZ_LOG_TEST(gSHLog, LogLevel::Debug)) {
+    return;
+  }
+
+  MOZ_LOG(gSHLog, LogLevel::Debug, ("nsSHistory %p\n", this));
+  int32_t length = Length();
+  for (int32_t i = 0; i < length; i++) {
+    LogEntry(mEntries[i], i, length, EmptyCString(), i == mIndex);
+  }
+}
+
+void nsSHistory::WindowIndices(int32_t aIndex, int32_t* aOutStartIndex,
+                               int32_t* aOutEndIndex) {
+  *aOutStartIndex = std::max(0, aIndex - nsSHistory::VIEWER_WINDOW);
+  *aOutEndIndex = std::min(Length() - 1, aIndex + nsSHistory::VIEWER_WINDOW);
+}
+
+NS_IMETHODIMP
+nsSHistory::PurgeHistory(int32_t aNumEntries) {
+  if (Length() <= 0 || aNumEntries <= 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  SHistoryChangeNotifier change(this);
+
+  aNumEntries = std::min(aNumEntries, Length());
+
+  NOTIFY_LISTENERS(OnHistoryPurge, ());
+
+  // Remove the first `aNumEntries` entries.
+  mEntries.RemoveElementsAt(0, aNumEntries);
+
+  // Adjust the indices, but don't let them go below -1.
+  mIndex -= aNumEntries;
+  mIndex = std::max(mIndex, -1);
+  mRequestedIndex -= aNumEntries;
+  mRequestedIndex = std::max(mRequestedIndex, -1);
+
+  if (mRootBC && mRootBC->GetDocShell()) {
+    mRootBC->GetDocShell()->HistoryPurged(aNumEntries);
+  }
+
+  UpdateRootBrowsingContextState();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::AddSHistoryListener(nsISHistoryListener* aListener) {
+  NS_ENSURE_ARG_POINTER(aListener);
+
+  // Check if the listener supports Weak Reference. This is a must.
+  // This listener functionality is used by embedders and we want to
+  // have the right ownership with who ever listens to SHistory
+  nsWeakPtr listener = do_GetWeakReference(aListener);
+  if (!listener) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mListeners.AppendElementUnlessExists(listener);
+  return NS_OK;
+}
+
+void nsSHistory::NotifyListenersContentViewerEvicted(uint32_t aNumEvicted) {
+  NOTIFY_LISTENERS(OnContentViewerEvicted, (aNumEvicted));
+}
+
+NS_IMETHODIMP
+nsSHistory::RemoveSHistoryListener(nsISHistoryListener* aListener) {
+  // Make sure the listener that wants to be removed is the
+  // one we have in store.
+  nsWeakPtr listener = do_GetWeakReference(aListener);
+  mListeners.RemoveElement(listener);
+  return NS_OK;
+}
+
+/* Replace an entry in the History list at a particular index.
+ * Do not update index or count.
+ */
+NS_IMETHODIMP
+nsSHistory::ReplaceEntry(int32_t aIndex, nsISHEntry* aReplaceEntry) {
+  NS_ENSURE_ARG(aReplaceEntry);
+
+  if (aIndex < 0 || aIndex >= Length()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsISHistory> shistoryOfEntry = aReplaceEntry->GetShistory();
+  if (shistoryOfEntry && shistoryOfEntry != this) {
+    NS_WARNING(
+        "The entry has been associated to another nsISHistory instance. "
+        "Try nsISHEntry.clone() and nsISHEntry.abandonBFCacheEntry() "
+        "first if you're copying an entry from another nsISHistory.");
+    return NS_ERROR_FAILURE;
+  }
+
+  aReplaceEntry->SetShistory(this);
+
+  NOTIFY_LISTENERS(OnHistoryReplaceEntry, ());
+
+  aReplaceEntry->SetPersist(true);
+  mEntries[aIndex] = aReplaceEntry;
+
+  UpdateRootBrowsingContextState();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::NotifyOnHistoryReload(bool* aCanReload) {
+  NOTIFY_LISTENERS_CANCELABLE(OnHistoryReload, *aCanReload, (aCanReload));
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::EvictOutOfRangeContentViewers(int32_t aIndex) {
+  // Check our per SHistory object limit in the currently navigated SHistory
+  EvictOutOfRangeWindowContentViewers(aIndex);
+  // Check our total limit across all SHistory objects
+  GloballyEvictContentViewers();
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(void)
+nsSHistory::EvictContentViewersOrReplaceEntry(nsISHEntry* aNewSHEntry,
+                                              bool aReplace) {
+  if (!aReplace) {
+    int32_t curIndex;
+    GetIndex(&curIndex);
+    if (curIndex > -1) {
+      EvictOutOfRangeContentViewers(curIndex);
+    }
+  } else {
+    nsCOMPtr<nsISHEntry> rootSHEntry = nsSHistory::GetRootSHEntry(aNewSHEntry);
+
+    int32_t index = GetIndexOfEntry(rootSHEntry);
+    if (index > -1) {
+      ReplaceEntry(index, rootSHEntry);
+    }
+  }
+}
+
+NS_IMETHODIMP
+nsSHistory::EvictAllContentViewers() {
+  // XXXbz we don't actually do a good job of evicting things as we should, so
+  // we might have viewers quite far from mIndex.  So just evict everything.
+  for (int32_t i = 0; i < Length(); i++) {
+    EvictContentViewerForEntry(mEntries[i]);
+  }
+
+  return NS_OK;
+}
+
+/* static */
+void nsSHistory::LoadURIs(nsTArray<LoadEntryResult>& aLoadResults) {
+  for (LoadEntryResult& loadEntry : aLoadResults) {
+    loadEntry.mBrowsingContext->LoadURI(loadEntry.mLoadState, false);
+  }
+}
+
+NS_IMETHODIMP
+nsSHistory::Reload(uint32_t aReloadFlags) {
+  nsTArray<LoadEntryResult> loadResults;
+  nsresult rv = Reload(aReloadFlags, loadResults);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (loadResults.IsEmpty()) {
+    return NS_OK;
+  }
+
+  LoadURIs(loadResults);
+  return NS_OK;
+}
+
+nsresult nsSHistory::Reload(uint32_t aReloadFlags,
+                            nsTArray<LoadEntryResult>& aLoadResults) {
+  MOZ_ASSERT(aLoadResults.IsEmpty());
+
+  uint32_t loadType;
+  if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_BYPASS_PROXY &&
+      aReloadFlags & nsIWebNavigation::LOAD_FLAGS_BYPASS_CACHE) {
+    loadType = LOAD_RELOAD_BYPASS_PROXY_AND_CACHE;
+  } else if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_BYPASS_PROXY) {
+    loadType = LOAD_RELOAD_BYPASS_PROXY;
+  } else if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_BYPASS_CACHE) {
+    loadType = LOAD_RELOAD_BYPASS_CACHE;
+  } else if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_CHARSET_CHANGE) {
+    loadType = LOAD_RELOAD_CHARSET_CHANGE;
+  } else if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_ALLOW_MIXED_CONTENT) {
+    loadType = LOAD_RELOAD_ALLOW_MIXED_CONTENT;
+  } else {
+    loadType = LOAD_RELOAD_NORMAL;
+  }
+
+  // We are reloading. Send Reload notifications.
+  // nsDocShellLoadFlagType is not public, where as nsIWebNavigation
+  // is public. So send the reload notifications with the
+  // nsIWebNavigation flags.
+  bool canNavigate = true;
+  NOTIFY_LISTENERS_CANCELABLE(OnHistoryReload, canNavigate, (&canNavigate));
+  if (!canNavigate) {
+    return NS_OK;
+  }
+
+  nsresult rv = LoadEntry(mIndex, loadType, HIST_CMD_RELOAD, aLoadResults);
+  if (NS_FAILED(rv)) {
+    aLoadResults.Clear();
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::ReloadCurrentEntry() {
+  nsTArray<LoadEntryResult> loadResults;
+  nsresult rv = ReloadCurrentEntry(loadResults);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  LoadURIs(loadResults);
+  return NS_OK;
+}
+
+nsresult nsSHistory::ReloadCurrentEntry(
+    nsTArray<LoadEntryResult>& aLoadResults) {
+  // Notify listeners
+  NOTIFY_LISTENERS(OnHistoryGotoIndex, ());
+
+  return LoadEntry(mIndex, LOAD_HISTORY, HIST_CMD_RELOAD, aLoadResults);
+}
+
+void nsSHistory::EvictOutOfRangeWindowContentViewers(int32_t aIndex) {
+  // XXX rename method to EvictContentViewersExceptAroundIndex, or something.
+
+  // We need to release all content viewers that are no longer in the range
+  //
+  //  aIndex - VIEWER_WINDOW to aIndex + VIEWER_WINDOW
+  //
+  // to ensure that this SHistory object isn't responsible for more than
+  // VIEWER_WINDOW content viewers.  But our job is complicated by the
+  // fact that two entries which are related by either hash navigations or
+  // history.pushState will have the same content viewer.
+  //
+  // To illustrate the issue, suppose VIEWER_WINDOW = 3 and we have four
+  // linked entries in our history.  Suppose we then add a new content
+  // viewer and call into this function.  So the history looks like:
+  //
+  //   A A A A B
+  //     +     *
+  //
+  // where the letters are content viewers and + and * denote the beginning and
+  // end of the range aIndex +/- VIEWER_WINDOW.
+  //
+  // Although one copy of the content viewer A exists outside the range, we
+  // don't want to evict A, because it has other copies in range!
+  //
+  // We therefore adjust our eviction strategy to read:
+  //
+  //   Evict each content viewer outside the range aIndex -/+
+  //   VIEWER_WINDOW, unless that content viewer also appears within the
+  //   range.
+  //
+  // (Note that it's entirely legal to have two copies of one content viewer
+  // separated by a different content viewer -- call pushState twice, go back
+  // once, and refresh -- so we can't rely on identical viewers only appearing
+  // adjacent to one another.)
+
+  if (aIndex < 0) {
+    return;
+  }
+  NS_ENSURE_TRUE_VOID(aIndex < Length());
+
+  // Calculate the range that's safe from eviction.
+  int32_t startSafeIndex, endSafeIndex;
+  WindowIndices(aIndex, &startSafeIndex, &endSafeIndex);
+
+  LOG(
+      ("EvictOutOfRangeWindowContentViewers(index=%d), "
+       "Length()=%d. Safe range [%d, %d]",
+       aIndex, Length(), startSafeIndex, endSafeIndex));
+
+  // The content viewers in range aIndex -/+ VIEWER_WINDOW will not be
+  // evicted.  Collect a set of them so we don't accidentally evict one of them
+  // if it appears outside this range.
+  nsCOMArray<nsIContentViewer> safeViewers;
+  for (int32_t i = startSafeIndex; i <= endSafeIndex; i++) {
+    nsCOMPtr<nsIContentViewer> viewer = mEntries[i]->GetContentViewer();
+    safeViewers.AppendObject(viewer);
+  }
+
+  // Walk the SHistory list and evict any content viewers that aren't safe.
+  // (It's important that the condition checks Length(), rather than a cached
+  // copy of Length(), because the length might change between iterations.)
+  for (int32_t i = 0; i < Length(); i++) {
+    nsCOMPtr<nsISHEntry> entry = mEntries[i];
+    nsCOMPtr<nsIContentViewer> viewer = entry->GetContentViewer();
+    if (safeViewers.IndexOf(viewer) == -1) {
+      EvictContentViewerForEntry(entry);
+    }
+  }
+}
+
+namespace {
+
+class EntryAndDistance {
+ public:
+  EntryAndDistance(nsSHistory* aSHistory, nsISHEntry* aEntry, uint32_t aDist)
+      : mSHistory(aSHistory),
+        mEntry(aEntry),
+        mViewer(aEntry->GetContentViewer()),
+        mLastTouched(mEntry->GetLastTouched()),
+        mDistance(aDist) {
+    NS_ASSERTION(mViewer, "Entry should have a content viewer");
+  }
+
+  bool operator<(const EntryAndDistance& aOther) const {
+    // Compare distances first, and fall back to last-accessed times.
+    if (aOther.mDistance != this->mDistance) {
+      return this->mDistance < aOther.mDistance;
+    }
+
+    return this->mLastTouched < aOther.mLastTouched;
+  }
+
+  bool operator==(const EntryAndDistance& aOther) const {
+    // This is a little silly; we need == so the default comaprator can be
+    // instantiated, but this function is never actually called when we sort
+    // the list of EntryAndDistance objects.
+    return aOther.mDistance == this->mDistance &&
+           aOther.mLastTouched == this->mLastTouched;
+  }
+
+  RefPtr<nsSHistory> mSHistory;
+  nsCOMPtr<nsISHEntry> mEntry;
+  nsCOMPtr<nsIContentViewer> mViewer;
+  uint32_t mLastTouched;
+  int32_t mDistance;
+};
+
+}  // namespace
+
+// static
+void nsSHistory::GloballyEvictContentViewers() {
+  // First, collect from each SHistory object the entries which have a cached
+  // content viewer. Associate with each entry its distance from its SHistory's
+  // current index.
+
+  nsTArray<EntryAndDistance> entries;
+
+  for (auto shist : gSHistoryList) {
+    // FIXME Bug 1546348: Make global eviction work for session history in the
+    //       parent and remove mIsRemote.
+    if (shist->mIsRemote) {
+      continue;
+    }
+
+    // Maintain a list of the entries which have viewers and belong to
+    // this particular shist object.  We'll add this list to the global list,
+    // |entries|, eventually.
+    nsTArray<EntryAndDistance> shEntries;
+
+    // Content viewers are likely to exist only within shist->mIndex -/+
+    // VIEWER_WINDOW, so only search within that range.
+    //
+    // A content viewer might exist outside that range due to either:
+    //
+    //   * history.pushState or hash navigations, in which case a copy of the
+    //     content viewer should exist within the range, or
+    //
+    //   * bugs which cause us not to call nsSHistory::EvictContentViewers()
+    //     often enough.  Once we do call EvictContentViewers() for the
+    //     SHistory object in question, we'll do a full search of its history
+    //     and evict the out-of-range content viewers, so we don't bother here.
+    //
+    int32_t startIndex, endIndex;
+    shist->WindowIndices(shist->mIndex, &startIndex, &endIndex);
+    for (int32_t i = startIndex; i <= endIndex; i++) {
+      nsCOMPtr<nsISHEntry> entry = shist->mEntries[i];
+      nsCOMPtr<nsIContentViewer> contentViewer = entry->GetContentViewer();
+
+      if (contentViewer) {
+        // Because one content viewer might belong to multiple SHEntries, we
+        // have to search through shEntries to see if we already know
+        // about this content viewer.  If we find the viewer, update its
+        // distance from the SHistory's index and continue.
+        bool found = false;
+        for (uint32_t j = 0; j < shEntries.Length(); j++) {
+          EntryAndDistance& container = shEntries[j];
+          if (container.mViewer == contentViewer) {
+            container.mDistance =
+                std::min(container.mDistance, DeprecatedAbs(i - shist->mIndex));
+            found = true;
+            break;
+          }
+        }
+
+        // If we didn't find a EntryAndDistance for this content viewer, make a
+        // new one.
+        if (!found) {
+          EntryAndDistance container(shist, entry,
+                                     DeprecatedAbs(i - shist->mIndex));
+          shEntries.AppendElement(container);
+        }
+      }
+    }
+
+    // We've found all the entries belonging to shist which have viewers.
+    // Add those entries to our global list and move on.
+    entries.AppendElements(shEntries);
+  }
+
+  // We now have collected all cached content viewers.  First check that we
+  // have enough that we actually need to evict some.
+  if ((int32_t)entries.Length() <= sHistoryMaxTotalViewers) {
+    return;
+  }
+
+  // If we need to evict, sort our list of entries and evict the largest
+  // ones.  (We could of course get better algorithmic complexity here by using
+  // a heap or something more clever.  But sHistoryMaxTotalViewers isn't large,
+  // so let's not worry about it.)
+  entries.Sort();
+
+  for (int32_t i = entries.Length() - 1; i >= sHistoryMaxTotalViewers; --i) {
+    (entries[i].mSHistory)->EvictContentViewerForEntry(entries[i].mEntry);
+  }
+}
+
+nsresult nsSHistory::FindEntryForBFCache(nsIBFCacheEntry* aBFEntry,
+                                         nsISHEntry** aResult,
+                                         int32_t* aResultIndex) {
+  *aResult = nullptr;
+  *aResultIndex = -1;
+
+  int32_t startIndex, endIndex;
+  WindowIndices(mIndex, &startIndex, &endIndex);
+
+  for (int32_t i = startIndex; i <= endIndex; ++i) {
+    nsCOMPtr<nsISHEntry> shEntry = mEntries[i];
+
+    // Does shEntry have the same BFCacheEntry as the argument to this method?
+    if (shEntry->HasBFCacheEntry(aBFEntry)) {
+      shEntry.forget(aResult);
+      *aResultIndex = i;
+      return NS_OK;
+    }
+  }
+  return NS_ERROR_FAILURE;
+}
+
+nsresult nsSHistory::EvictExpiredContentViewerForEntry(
+    nsIBFCacheEntry* aBFEntry) {
+  int32_t index;
+  nsCOMPtr<nsISHEntry> shEntry;
+  FindEntryForBFCache(aBFEntry, getter_AddRefs(shEntry), &index);
+
+  if (index == mIndex) {
+    NS_WARNING("How did the current SHEntry expire?");
+    return NS_OK;
+  }
+
+  if (shEntry) {
+    EvictContentViewerForEntry(shEntry);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(void)
+nsSHistory::AddToExpirationTracker(nsIBFCacheEntry* aBFEntry) {
+  RefPtr<nsSHEntryShared> entry = static_cast<nsSHEntryShared*>(aBFEntry);
+  if (!mHistoryTracker || !entry) {
+    return;
+  }
+
+  mHistoryTracker->AddObject(entry);
+  return;
+}
+
+NS_IMETHODIMP_(void)
+nsSHistory::RemoveFromExpirationTracker(nsIBFCacheEntry* aBFEntry) {
+  RefPtr<nsSHEntryShared> entry = static_cast<nsSHEntryShared*>(aBFEntry);
+  MOZ_ASSERT(mHistoryTracker && !mHistoryTracker->IsEmpty());
+  if (!mHistoryTracker || !entry) {
+    return;
+  }
+
+  mHistoryTracker->RemoveObject(entry);
+}
+
+// Evicts all content viewers in all history objects.  This is very
+// inefficient, because it requires a linear search through all SHistory
+// objects for each viewer to be evicted.  However, this method is called
+// infrequently -- only when the disk or memory cache is cleared.
+
+// static
+void nsSHistory::GloballyEvictAllContentViewers() {
+  int32_t maxViewers = sHistoryMaxTotalViewers;
+  sHistoryMaxTotalViewers = 0;
+  GloballyEvictContentViewers();
+  sHistoryMaxTotalViewers = maxViewers;
+}
+
+void GetDynamicChildren(nsISHEntry* aEntry, nsTArray<nsID>& aDocshellIDs) {
+  int32_t count = aEntry->GetChildCount();
+  for (int32_t i = 0; i < count; ++i) {
+    nsCOMPtr<nsISHEntry> child;
+    aEntry->GetChildAt(i, getter_AddRefs(child));
+    if (child) {
+      if (child->IsDynamicallyAdded()) {
+        child->GetDocshellID(*aDocshellIDs.AppendElement());
+      } else {
+        GetDynamicChildren(child, aDocshellIDs);
+      }
+    }
+  }
+}
+
+bool RemoveFromSessionHistoryEntry(nsISHEntry* aRoot,
+                                   nsTArray<nsID>& aDocshellIDs) {
+  bool didRemove = false;
+  int32_t childCount = aRoot->GetChildCount();
+  for (int32_t i = childCount - 1; i >= 0; --i) {
+    nsCOMPtr<nsISHEntry> child;
+    aRoot->GetChildAt(i, getter_AddRefs(child));
+    if (child) {
+      nsID docshelldID;
+      child->GetDocshellID(docshelldID);
+      if (aDocshellIDs.Contains(docshelldID)) {
+        didRemove = true;
+        aRoot->RemoveChild(child);
+      } else if (RemoveFromSessionHistoryEntry(child, aDocshellIDs)) {
+        didRemove = true;
+      }
+    }
+  }
+  return didRemove;
+}
+
+bool RemoveChildEntries(nsISHistory* aHistory, int32_t aIndex,
+                        nsTArray<nsID>& aEntryIDs) {
+  nsCOMPtr<nsISHEntry> root;
+  aHistory->GetEntryAtIndex(aIndex, getter_AddRefs(root));
+  return root ? RemoveFromSessionHistoryEntry(root, aEntryIDs) : false;
+}
+
+bool IsSameTree(nsISHEntry* aEntry1, nsISHEntry* aEntry2) {
+  if (!aEntry1 && !aEntry2) {
+    return true;
+  }
+  if ((!aEntry1 && aEntry2) || (aEntry1 && !aEntry2)) {
+    return false;
+  }
+  uint32_t id1 = aEntry1->GetID();
+  uint32_t id2 = aEntry2->GetID();
+  if (id1 != id2) {
+    return false;
+  }
+
+  int32_t count1 = aEntry1->GetChildCount();
+  int32_t count2 = aEntry2->GetChildCount();
+  // We allow null entries in the end of the child list.
+  int32_t count = std::max(count1, count2);
+  for (int32_t i = 0; i < count; ++i) {
+    nsCOMPtr<nsISHEntry> child1, child2;
+    aEntry1->GetChildAt(i, getter_AddRefs(child1));
+    aEntry2->GetChildAt(i, getter_AddRefs(child2));
+    if (!IsSameTree(child1, child2)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool nsSHistory::RemoveDuplicate(int32_t aIndex, bool aKeepNext) {
+  NS_ASSERTION(aIndex >= 0, "aIndex must be >= 0!");
+  NS_ASSERTION(aIndex != 0 || aKeepNext,
+               "If we're removing index 0 we must be keeping the next");
+  NS_ASSERTION(aIndex != mIndex, "Shouldn't remove mIndex!");
+
+  int32_t compareIndex = aKeepNext ? aIndex + 1 : aIndex - 1;
+
+  nsresult rv;
+  nsCOMPtr<nsISHEntry> root1, root2;
+  rv = GetEntryAtIndex(aIndex, getter_AddRefs(root1));
+  if (NS_FAILED(rv)) {
+    return false;
+  }
+  rv = GetEntryAtIndex(compareIndex, getter_AddRefs(root2));
+  if (NS_FAILED(rv)) {
+    return false;
+  }
+
+  SHistoryChangeNotifier change(this);
+
+  if (IsSameTree(root1, root2)) {
+    mEntries.RemoveElementAt(aIndex);
+
+    // FIXME Bug 1546350: Reimplement history listeners.
+    // if (mRootBC && mRootBC->GetDocShell()) {
+    //  static_cast<nsDocShell*>(mRootBC->GetDocShell())
+    //      ->HistoryEntryRemoved(aIndex);
+    //}
+
+    // Adjust our indices to reflect the removed entry.
+    if (mIndex > aIndex) {
+      mIndex = mIndex - 1;
+    }
+
+    // NB: If the entry we are removing is the entry currently
+    // being navigated to (mRequestedIndex) then we adjust the index
+    // only if we're not keeping the next entry (because if we are keeping
+    // the next entry (because the current is a duplicate of the next), then
+    // that entry slides into the spot that we're currently pointing to.
+    // We don't do this adjustment for mIndex because mIndex cannot equal
+    // aIndex.
+
+    // NB: We don't need to guard on mRequestedIndex being nonzero here,
+    // because either they're strictly greater than aIndex which is at least
+    // zero, or they are equal to aIndex in which case aKeepNext must be true
+    // if aIndex is zero.
+    if (mRequestedIndex > aIndex || (mRequestedIndex == aIndex && !aKeepNext)) {
+      mRequestedIndex = mRequestedIndex - 1;
+    }
+
+    return true;
+  }
+  return false;
+}
+
+NS_IMETHODIMP_(void)
+nsSHistory::RemoveEntries(nsTArray<nsID>& aIDs, int32_t aStartIndex) {
+  bool didRemove;
+  RemoveEntries(aIDs, aStartIndex, &didRemove);
+  if (didRemove && mRootBC && mRootBC->GetDocShell()) {
+    mRootBC->GetDocShell()->DispatchLocationChangeEvent();
+  }
+}
+
+void nsSHistory::RemoveEntries(nsTArray<nsID>& aIDs, int32_t aStartIndex,
+                               bool* aDidRemove) {
+  SHistoryChangeNotifier change(this);
+
+  int32_t index = aStartIndex;
+  while (index >= 0 && RemoveChildEntries(this, --index, aIDs)) {
+  }
+  int32_t minIndex = index;
+  index = aStartIndex;
+  while (index >= 0 && RemoveChildEntries(this, index++, aIDs)) {
+  }
+
+  // We need to remove duplicate nsSHEntry trees.
+  *aDidRemove = false;
+  while (index > minIndex) {
+    if (index != mIndex && RemoveDuplicate(index, index < mIndex)) {
+      *aDidRemove = true;
+    }
+    --index;
+  }
+
+  UpdateRootBrowsingContextState();
+}
+
+void nsSHistory::RemoveFrameEntries(nsISHEntry* aEntry) {
+  int32_t count = aEntry->GetChildCount();
+  AutoTArray<nsID, 16> ids;
+  for (int32_t i = 0; i < count; ++i) {
+    nsCOMPtr<nsISHEntry> child;
+    aEntry->GetChildAt(i, getter_AddRefs(child));
+    if (child) {
+      child->GetDocshellID(*ids.AppendElement());
+    }
+  }
+  RemoveEntries(ids, mIndex);
+}
+
+void nsSHistory::RemoveDynEntries(int32_t aIndex, nsISHEntry* aEntry) {
+  // Remove dynamic entries which are at the index and belongs to the container.
+  nsCOMPtr<nsISHEntry> entry(aEntry);
+  if (!entry) {
+    GetEntryAtIndex(aIndex, getter_AddRefs(entry));
+  }
+
+  if (entry) {
+    AutoTArray<nsID, 16> toBeRemovedEntries;
+    GetDynamicChildren(entry, toBeRemovedEntries);
+    if (toBeRemovedEntries.Length()) {
+      RemoveEntries(toBeRemovedEntries, aIndex);
+    }
+  }
+}
+
+void nsSHistory::RemoveDynEntriesForBFCacheEntry(nsIBFCacheEntry* aBFEntry) {
+  int32_t index;
+  nsCOMPtr<nsISHEntry> shEntry;
+  FindEntryForBFCache(aBFEntry, getter_AddRefs(shEntry), &index);
+  if (shEntry) {
+    RemoveDynEntries(index, shEntry);
+  }
+}
+
+NS_IMETHODIMP
+nsSHistory::UpdateIndex() {
+  SHistoryChangeNotifier change(this);
+
+  // Update the actual index with the right value.
+  if (mIndex != mRequestedIndex && mRequestedIndex != -1) {
+    mIndex = mRequestedIndex;
+  }
+
+  mRequestedIndex = -1;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GotoIndex(int32_t aIndex) {
+  nsTArray<LoadEntryResult> loadResults;
+  nsresult rv = GotoIndex(aIndex, loadResults);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  LoadURIs(loadResults);
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(void)
+nsSHistory::EnsureCorrectEntryAtCurrIndex(nsISHEntry* aEntry) {
+  int index = mRequestedIndex == -1 ? mIndex : mRequestedIndex;
+  if (index > -1 && (mEntries[index] != aEntry)) {
+    ReplaceEntry(index, aEntry);
+  }
+}
+
+nsresult nsSHistory::GotoIndex(int32_t aIndex,
+                               nsTArray<LoadEntryResult>& aLoadResults,
+                               bool aSameEpoch) {
+  return LoadEntry(aIndex, LOAD_HISTORY, HIST_CMD_GOTOINDEX, aLoadResults,
+                   aSameEpoch);
+}
+
+NS_IMETHODIMP_(bool)
+nsSHistory::HasUserInteractionAtIndex(int32_t aIndex) {
+  nsCOMPtr<nsISHEntry> entry;
+  GetEntryAtIndex(aIndex, getter_AddRefs(entry));
+  if (!entry) {
+    return false;
+  }
+  return entry->GetHasUserInteraction();
+}
+
+nsresult nsSHistory::LoadNextPossibleEntry(
+    int32_t aNewIndex, long aLoadType, uint32_t aHistCmd,
+    nsTArray<LoadEntryResult>& aLoadResults) {
+  mRequestedIndex = -1;
+  if (aNewIndex < mIndex) {
+    return LoadEntry(aNewIndex - 1, aLoadType, aHistCmd, aLoadResults);
+  }
+  if (aNewIndex > mIndex) {
+    return LoadEntry(aNewIndex + 1, aLoadType, aHistCmd, aLoadResults);
+  }
+  return NS_ERROR_FAILURE;
+}
+
+nsresult nsSHistory::LoadEntry(int32_t aIndex, long aLoadType,
+                               uint32_t aHistCmd,
+                               nsTArray<LoadEntryResult>& aLoadResults,
+                               bool aSameEpoch) {
+  MOZ_LOG(gSHistoryLog, LogLevel::Debug,
+          ("LoadEntry(%d, 0x%lx, %u)", aIndex, aLoadType, aHistCmd));
+  if (!mRootBC) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (aIndex < 0 || aIndex >= Length()) {
+    MOZ_LOG(gSHistoryLog, LogLevel::Debug, ("Index out of range"));
+    // The index is out of range
+    return NS_ERROR_FAILURE;
+  }
+
+  // This is a normal local history navigation.
+
+  nsCOMPtr<nsISHEntry> prevEntry;
+  nsCOMPtr<nsISHEntry> nextEntry;
+  GetEntryAtIndex(mIndex, getter_AddRefs(prevEntry));
+  GetEntryAtIndex(aIndex, getter_AddRefs(nextEntry));
+  if (!nextEntry || !prevEntry) {
+    mRequestedIndex = -1;
+    return NS_ERROR_FAILURE;
+  }
+
+  if (mozilla::SessionHistoryInParent()) {
+    if (aHistCmd == HIST_CMD_GOTOINDEX) {
+      // https://html.spec.whatwg.org/#history-traversal:
+      // To traverse the history
+      // "If entry has a different Document object than the current entry, then
+      // run the following substeps: Remove any tasks queued by the history
+      // traversal task source..."
+      //
+      // aSameEpoch is true only if the navigations would have been
+      // generated in the same spin of the event loop (i.e. history.go(-2);
+      // history.go(-1)) and from the same content process.
+      if (aSameEpoch) {
+        bool same_doc = false;
+        prevEntry->SharesDocumentWith(nextEntry, &same_doc);
+        if (!same_doc) {
+          MOZ_LOG(
+              gSHistoryLog, LogLevel::Debug,
+              ("Aborting GotoIndex %d - same epoch and not same doc", aIndex));
+          // Ignore this load. Before SessionHistoryInParent, this would
+          // have been dropped in InternalLoad after we filter out SameDoc
+          // loads.
+          return NS_ERROR_FAILURE;
+        }
+      }
+    }
+  }
+  // Keep note of requested history index in mRequestedIndex; after all bailouts
+  mRequestedIndex = aIndex;
+
+  // Remember that this entry is getting loaded at this point in the sequence
+
+  nextEntry->SetLastTouched(++gTouchCounter);
+
+  // Get the uri for the entry we are about to visit
+  nsCOMPtr<nsIURI> nextURI = nextEntry->GetURI();
+
+  MOZ_ASSERT(nextURI, "nextURI can't be null");
+
+  // Send appropriate listener notifications.
+  if (aHistCmd == HIST_CMD_GOTOINDEX) {
+    // We are going somewhere else. This is not reload either
+    NOTIFY_LISTENERS(OnHistoryGotoIndex, ());
+  }
+
+  if (mRequestedIndex == mIndex) {
+    // Possibly a reload case
+    InitiateLoad(nextEntry, mRootBC, aLoadType, aLoadResults);
+    return NS_OK;
+  }
+
+  // Going back or forward.
+  bool differenceFound = LoadDifferingEntries(prevEntry, nextEntry, mRootBC,
+                                              aLoadType, aLoadResults);
+  if (!differenceFound) {
+    // We did not find any differences. Go further in the history.
+    return LoadNextPossibleEntry(aIndex, aLoadType, aHistCmd, aLoadResults);
+  }
+
+  return NS_OK;
+}
+
+bool nsSHistory::LoadDifferingEntries(nsISHEntry* aPrevEntry,
+                                      nsISHEntry* aNextEntry,
+                                      BrowsingContext* aParent, long aLoadType,
+                                      nsTArray<LoadEntryResult>& aLoadResults) {
+  MOZ_ASSERT(aPrevEntry && aNextEntry && aParent);
+
+  uint32_t prevID = aPrevEntry->GetID();
+  uint32_t nextID = aNextEntry->GetID();
+
+  // Check the IDs to verify if the pages are different.
+  if (prevID != nextID) {
+    // Set the Subframe flag if not navigating the root docshell.
+    aNextEntry->SetIsSubFrame(aParent != mRootBC);
+    InitiateLoad(aNextEntry, aParent, aLoadType, aLoadResults);
+    return true;
+  }
+
+  // The entries are the same, so compare any child frames
+  int32_t pcnt = aPrevEntry->GetChildCount();
+  int32_t ncnt = aNextEntry->GetChildCount();
+
+  // Create an array for child browsing contexts.
+  nsTArray<RefPtr<BrowsingContext>> browsingContexts;
+  aParent->GetChildren(browsingContexts);
+
+  // Search for something to load next.
+  bool differenceFound = false;
+  for (int32_t i = 0; i < ncnt; ++i) {
+    // First get an entry which may cause a new page to be loaded.
+    nsCOMPtr<nsISHEntry> nChild;
+    aNextEntry->GetChildAt(i, getter_AddRefs(nChild));
+    if (!nChild) {
+      continue;
+    }
+    nsID docshellID;
+    nChild->GetDocshellID(docshellID);
+
+    // Then find the associated docshell.
+    RefPtr<BrowsingContext> bcChild;
+    for (const RefPtr<BrowsingContext>& bc : browsingContexts) {
+      if (bc->GetHistoryID() == docshellID) {
+        bcChild = bc;
+        break;
+      }
+    }
+    if (!bcChild) {
+      continue;
+    }
+
+    // Then look at the previous entries to see if there was
+    // an entry for the docshell.
+    nsCOMPtr<nsISHEntry> pChild;
+    for (int32_t k = 0; k < pcnt; ++k) {
+      nsCOMPtr<nsISHEntry> child;
+      aPrevEntry->GetChildAt(k, getter_AddRefs(child));
+      if (child) {
+        nsID dID;
+        child->GetDocshellID(dID);
+        if (dID == docshellID) {
+          pChild = child;
+          break;
+        }
+      }
+    }
+    if (!pChild) {
+      continue;
+    }
+
+    // Finally recursively call this method.
+    // This will either load a new page to shell or some subshell or
+    // do nothing.
+    if (LoadDifferingEntries(pChild, nChild, bcChild, aLoadType,
+                             aLoadResults)) {
+      differenceFound = true;
+    }
+  }
+  return differenceFound;
+}
+
+void nsSHistory::InitiateLoad(nsISHEntry* aFrameEntry,
+                              BrowsingContext* aFrameBC, long aLoadType,
+                              nsTArray<LoadEntryResult>& aLoadResults) {
+  MOZ_ASSERT(aFrameBC && aFrameEntry);
+
+  LoadEntryResult* loadResult = aLoadResults.AppendElement();
+  loadResult->mBrowsingContext = aFrameBC;
+
+  nsCOMPtr<nsIURI> newURI = aFrameEntry->GetURI();
+  RefPtr<nsDocShellLoadState> loadState = new nsDocShellLoadState(newURI);
+
+  /* Set the loadType in the SHEntry too to  what was passed on.
+   * This will be passed on to child subframes later in nsDocShell,
+   * so that proper loadType is maintained through out a frameset
+   */
+  aFrameEntry->SetLoadType(aLoadType);
+
+  loadState->SetLoadType(aLoadType);
+
+  loadState->SetSHEntry(aFrameEntry);
+
+  // If we're loading from the current active entry we want to treat it as not
+  // a same-document navigation (see nsDocShell::IsSameDocumentNavigation), so
+  // record that here in the LoadingSessionHistoryEntry.
+  bool loadingFromActiveEntry;
+  if (mozilla::SessionHistoryInParent()) {
+    loadingFromActiveEntry =
+        aFrameBC->Canonical()->GetActiveSessionHistoryEntry() == aFrameEntry;
+  } else {
+    loadingFromActiveEntry =
+        aFrameBC->GetDocShell() &&
+        nsDocShell::Cast(aFrameBC->GetDocShell())->IsOSHE(aFrameEntry);
+  }
+  loadState->SetLoadIsFromSessionHistory(mRequestedIndex, Length(),
+                                         loadingFromActiveEntry);
+
+  if (mozilla::SessionHistoryInParent()) {
+    nsCOMPtr<SessionHistoryEntry> she = do_QueryInterface(aFrameEntry);
+    aFrameBC->Canonical()->AddLoadingSessionHistoryEntry(
+        loadState->GetLoadingSessionHistoryInfo()->mLoadId, she);
+  }
+
+  nsCOMPtr<nsIURI> originalURI = aFrameEntry->GetOriginalURI();
+  loadState->SetOriginalURI(originalURI);
+
+  loadState->SetLoadReplace(aFrameEntry->GetLoadReplace());
+
+  loadState->SetLoadFlags(nsIWebNavigation::LOAD_FLAGS_NONE);
+  nsCOMPtr<nsIPrincipal> triggeringPrincipal =
+      aFrameEntry->GetTriggeringPrincipal();
+  loadState->SetTriggeringPrincipal(triggeringPrincipal);
+  loadState->SetFirstParty(false);
+  nsCOMPtr<nsIContentSecurityPolicy> csp = aFrameEntry->GetCsp();
+  loadState->SetCsp(csp);
+
+  loadResult->mLoadState = std::move(loadState);
+}
+
+NS_IMETHODIMP
+nsSHistory::CreateEntry(nsISHEntry** aEntry) {
+  nsCOMPtr<nsISHEntry> entry;
+  if (XRE_IsParentProcess() && mozilla::SessionHistoryInParent()) {
+    entry = new SessionHistoryEntry();
+  } else {
+    entry = new nsSHEntry();
+  }
+  entry.forget(aEntry);
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(bool)
+nsSHistory::IsEmptyOrHasEntriesForSingleTopLevelPage() {
+  if (mEntries.IsEmpty()) {
+    return true;
+  }
+
+  nsISHEntry* entry = mEntries[0];
+  size_t length = mEntries.Length();
+  for (size_t i = 1; i < length; ++i) {
+    bool sharesDocument = false;
+    mEntries[i]->SharesDocumentWith(entry, &sharesDocument);
+    if (!sharesDocument) {
+      return false;
+    }
+  }
+
+  return true;
+}