Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 2221 insertions, 0 deletions

diff --git a/dom/events/IMEContentObserver.cpp b/dom/events/IMEContentObserver.cpp
new file mode 100644
index 0000000000..a8d946933a
--- /dev/null
+++ b/dom/events/IMEContentObserver.cpp
@@ -0,0 +1,2221 @@
+/* -*- 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 "mozilla/Logging.h"
+
+#include "ContentEventHandler.h"
+#include "IMEContentObserver.h"
+#include "mozilla/AsyncEventDispatcher.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/EventStateManager.h"
+#include "mozilla/IMEStateManager.h"
+#include "mozilla/MouseEvents.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/TextComposition.h"
+#include "mozilla/TextControlElement.h"
+#include "mozilla/TextEvents.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/Selection.h"
+#include "nsContentUtils.h"
+#include "nsGkAtoms.h"
+#include "nsAtom.h"
+#include "nsDocShell.h"
+#include "nsIContent.h"
+#include "mozilla/dom/Document.h"
+#include "nsIFrame.h"
+#include "nsINode.h"
+#include "nsISelectionController.h"
+#include "nsISupports.h"
+#include "nsIWeakReferenceUtils.h"
+#include "nsIWidget.h"
+#include "nsPresContext.h"
+#include "nsRange.h"
+#include "nsRefreshDriver.h"
+#include "WritingModes.h"
+
+namespace mozilla {
+
+using RawNodePosition = ContentEventHandler::RawNodePosition;
+using RawNodePositionBefore = ContentEventHandler::RawNodePositionBefore;
+
+using namespace dom;
+using namespace widget;
+
+LazyLogModule sIMECOLog("IMEContentObserver");
+
+static const char* ToChar(bool aBool) { return aBool ? "true" : "false"; }
+
+// This method determines the node to use for the point before the current node.
+// If you have the following aContent and aContainer, and want to represent the
+// following point for `RawNodePosition` or `RawRangeBoundary`:
+//
+// <parent> {node} {node} | {node} </parent>
+//  ^                     ^     ^
+// aContainer           point  aContent
+//
+// This function will shift `aContent` to the left into the format which
+// `RawNodePosition` and `RawRangeBoundary` use:
+//
+// <parent> {node} {node} | {node} </parent>
+//  ^               ^     ^
+// aContainer    result  point
+static nsIContent* PointBefore(nsINode* aContainer, nsIContent* aContent) {
+  if (aContent) {
+    return aContent->GetPreviousSibling();
+  }
+  return aContainer->GetLastChild();
+}
+
+/******************************************************************************
+ * mozilla::IMEContentObserver
+ ******************************************************************************/
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(IMEContentObserver)
+
+// Note that we don't need to add mFirstAddedContainer nor
+// mLastAddedContainer to cycle collection because they are non-null only
+// during short time and shouldn't be touched while they are non-null.
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(IMEContentObserver)
+  nsAutoScriptBlocker scriptBlocker;
+
+  tmp->NotifyIMEOfBlur();
+  tmp->UnregisterObservers();
+
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mSelection)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mRootElement)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mEditableNode)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mDocShell)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mEditorBase)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mDocumentObserver)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mEndOfAddedTextCache.mContainerNode)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mStartOfRemovingTextRangeCache.mContainerNode)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_REFERENCE
+
+  tmp->mIMENotificationRequests = nullptr;
+  tmp->mESM = nullptr;
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(IMEContentObserver)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mWidget)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFocusedWidget)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mSelection)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mRootElement)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mEditableNode)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDocShell)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mEditorBase)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDocumentObserver)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mEndOfAddedTextCache.mContainerNode)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(
+      mStartOfRemovingTextRangeCache.mContainerNode)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(IMEContentObserver)
+  NS_INTERFACE_MAP_ENTRY(nsIMutationObserver)
+  NS_INTERFACE_MAP_ENTRY(nsIReflowObserver)
+  NS_INTERFACE_MAP_ENTRY(nsIScrollObserver)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIReflowObserver)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(IMEContentObserver)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(IMEContentObserver)
+
+IMEContentObserver::IMEContentObserver() {
+#ifdef DEBUG
+  // TODO: Make this test as GTest.
+  mTextChangeData.Test();
+#endif
+}
+
+void IMEContentObserver::Init(nsIWidget& aWidget, nsPresContext& aPresContext,
+                              Element* aElement, EditorBase& aEditorBase) {
+  State state = GetState();
+  if (NS_WARN_IF(state == eState_Observing)) {
+    return;  // Nothing to do.
+  }
+
+  bool firstInitialization = state != eState_StoppedObserving;
+  if (!firstInitialization) {
+    // If this is now trying to initialize with new contents, all observers
+    // should be registered again for simpler implementation.
+    UnregisterObservers();
+    Clear();
+  }
+
+  mESM = aPresContext.EventStateManager();
+  mESM->OnStartToObserveContent(this);
+
+  mWidget = &aWidget;
+  mIMENotificationRequests = &mWidget->IMENotificationRequestsRef();
+
+  if (!InitWithEditor(aPresContext, aElement, aEditorBase)) {
+    MOZ_LOG(sIMECOLog, LogLevel::Error,
+            ("0x%p   Init() FAILED, due to InitWithEditor() "
+             "failure",
+             this));
+    Clear();
+    return;
+  }
+
+  if (firstInitialization) {
+    // Now, try to send NOTIFY_IME_OF_FOCUS to IME via the widget.
+    MaybeNotifyIMEOfFocusSet();
+    // When this is called first time, IME has not received NOTIFY_IME_OF_FOCUS
+    // yet since NOTIFY_IME_OF_FOCUS will be sent to widget asynchronously.
+    // So, we need to do nothing here.  After NOTIFY_IME_OF_FOCUS has been
+    // sent, OnIMEReceivedFocus() will be called and content, selection and/or
+    // position changes will be observed
+    return;
+  }
+
+  // When this is called after editor reframing (i.e., the root editable node
+  // is also recreated), IME has usually received NOTIFY_IME_OF_FOCUS.  In this
+  // case, we need to restart to observe content, selection and/or position
+  // changes in new root editable node.
+  ObserveEditableNode();
+
+  if (!NeedsToNotifyIMEOfSomething()) {
+    return;
+  }
+
+  // Some change events may wait to notify IME because this was being
+  // initialized.  It is the time to flush them.
+  FlushMergeableNotifications();
+}
+
+void IMEContentObserver::OnIMEReceivedFocus() {
+  // While Init() notifies IME of focus, pending layout may be flushed
+  // because the notification may cause querying content.  Then, recursive
+  // call of Init() with the latest content may occur.  In such case, we
+  // shouldn't keep first initialization which notified IME of focus.
+  if (GetState() != eState_Initializing) {
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   OnIMEReceivedFocus(), "
+             "but the state is not \"initializing\", so does nothing",
+             this));
+    return;
+  }
+
+  // NOTIFY_IME_OF_FOCUS might cause recreating IMEContentObserver
+  // instance via IMEStateManager::UpdateIMEState().  So, this
+  // instance might already have been destroyed, check it.
+  if (!mRootElement) {
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   OnIMEReceivedFocus(), "
+             "but mRootElement has already been cleared, so does nothing",
+             this));
+    return;
+  }
+
+  // Start to observe which is needed by IME when IME actually has focus.
+  ObserveEditableNode();
+
+  if (!NeedsToNotifyIMEOfSomething()) {
+    return;
+  }
+
+  // Some change events may wait to notify IME because this was being
+  // initialized.  It is the time to flush them.
+  FlushMergeableNotifications();
+}
+
+bool IMEContentObserver::InitWithEditor(nsPresContext& aPresContext,
+                                        Element* aElement,
+                                        EditorBase& aEditorBase) {
+  mEditableNode = IMEStateManager::GetRootEditableNode(aPresContext, aElement);
+  if (NS_WARN_IF(!mEditableNode)) {
+    return false;
+  }
+
+  mEditorBase = &aEditorBase;
+
+  RefPtr<PresShell> presShell = aPresContext.GetPresShell();
+
+  // get selection and root content
+  nsCOMPtr<nsISelectionController> selCon;
+  if (mEditableNode->IsContent()) {
+    nsIFrame* frame = mEditableNode->AsContent()->GetPrimaryFrame();
+    if (NS_WARN_IF(!frame)) {
+      return false;
+    }
+
+    frame->GetSelectionController(&aPresContext, getter_AddRefs(selCon));
+  } else {
+    // mEditableNode is a document
+    selCon = presShell;
+  }
+
+  if (NS_WARN_IF(!selCon)) {
+    return false;
+  }
+
+  mSelection = selCon->GetSelection(nsISelectionController::SELECTION_NORMAL);
+  if (NS_WARN_IF(!mSelection)) {
+    return false;
+  }
+
+  if (mEditorBase->IsTextEditor()) {
+    mRootElement = mEditorBase->GetRoot();  // The anonymous <div>
+    MOZ_ASSERT(mRootElement);
+    MOZ_ASSERT(mRootElement->GetFirstChild());
+    if (auto* text = Text::FromNodeOrNull(
+            mRootElement ? mRootElement->GetFirstChild() : nullptr)) {
+      mTextControlValueLength = ContentEventHandler::GetNativeTextLength(*text);
+    }
+    mIsTextControl = true;
+  } else if (const nsRange* selRange = mSelection->GetRangeAt(0)) {
+    MOZ_ASSERT(!mIsTextControl);
+    if (NS_WARN_IF(!selRange->GetStartContainer())) {
+      return false;
+    }
+
+    nsCOMPtr<nsINode> startContainer = selRange->GetStartContainer();
+    mRootElement = Element::FromNodeOrNull(
+        startContainer->GetSelectionRootContent(presShell));
+  } else {
+    MOZ_ASSERT(!mIsTextControl);
+    nsCOMPtr<nsINode> editableNode = mEditableNode;
+    mRootElement = Element::FromNodeOrNull(
+        editableNode->GetSelectionRootContent(presShell));
+  }
+  if (!mRootElement && mEditableNode->IsDocument()) {
+    // The document node is editable, but there are no contents, this document
+    // is not editable.
+    return false;
+  }
+
+  if (NS_WARN_IF(!mRootElement)) {
+    return false;
+  }
+
+  mDocShell = aPresContext.GetDocShell();
+  if (NS_WARN_IF(!mDocShell)) {
+    return false;
+  }
+
+  mDocumentObserver = new DocumentObserver(*this);
+
+  return true;
+}
+
+void IMEContentObserver::Clear() {
+  mEditorBase = nullptr;
+  mSelection = nullptr;
+  mEditableNode = nullptr;
+  mRootElement = nullptr;
+  mDocShell = nullptr;
+  // Should be safe to clear mDocumentObserver here even though it grabs
+  // this instance in most cases because this is called by Init() or Destroy().
+  // The callers of Init() grab this instance with local RefPtr.
+  // The caller of Destroy() also grabs this instance with local RefPtr.
+  // So, this won't cause refcount of this instance become 0.
+  mDocumentObserver = nullptr;
+}
+
+void IMEContentObserver::ObserveEditableNode() {
+  MOZ_RELEASE_ASSERT(mSelection);
+  MOZ_RELEASE_ASSERT(mRootElement);
+  MOZ_RELEASE_ASSERT(GetState() != eState_Observing);
+
+  // If this is called before sending NOTIFY_IME_OF_FOCUS (it's possible when
+  // the editor is reframed before sending NOTIFY_IME_OF_FOCUS asynchronously),
+  // the notification requests of mWidget may be different from after the widget
+  // receives NOTIFY_IME_OF_FOCUS.   So, this should be called again by
+  // OnIMEReceivedFocus() which is called after sending NOTIFY_IME_OF_FOCUS.
+  if (!mIMEHasFocus) {
+    MOZ_ASSERT(!mWidget || mNeedsToNotifyIMEOfFocusSet ||
+                   mSendingNotification == NOTIFY_IME_OF_FOCUS,
+               "Wow, OnIMEReceivedFocus() won't be called?");
+    return;
+  }
+
+  mIsObserving = true;
+  if (mEditorBase) {
+    mEditorBase->SetIMEContentObserver(this);
+  }
+
+  mRootElement->AddMutationObserver(this);
+  // If it's in a document (should be so), we can use document observer to
+  // reduce redundant computation of text change offsets.
+  Document* doc = mRootElement->GetComposedDoc();
+  if (doc) {
+    RefPtr<DocumentObserver> documentObserver = mDocumentObserver;
+    documentObserver->Observe(doc);
+  }
+
+  if (mDocShell) {
+    // Add scroll position listener and reflow observer to detect position
+    // and size changes
+    mDocShell->AddWeakScrollObserver(this);
+    mDocShell->AddWeakReflowObserver(this);
+  }
+}
+
+void IMEContentObserver::NotifyIMEOfBlur() {
+  // Prevent any notifications to be sent IME.
+  nsCOMPtr<nsIWidget> widget;
+  mWidget.swap(widget);
+  mIMENotificationRequests = nullptr;
+
+  // If we hasn't been set focus, we shouldn't send blur notification to IME.
+  if (!mIMEHasFocus) {
+    return;
+  }
+
+  // mWidget must have been non-nullptr if IME has focus.
+  MOZ_RELEASE_ASSERT(widget);
+
+  RefPtr<IMEContentObserver> kungFuDeathGrip(this);
+
+  MOZ_LOG(sIMECOLog, LogLevel::Info,
+          ("0x%p NotifyIMEOfBlur(), sending NOTIFY_IME_OF_BLUR", this));
+
+  // For now, we need to send blur notification in any condition because
+  // we don't have any simple ways to send blur notification asynchronously.
+  // After this call, Destroy() or Unlink() will stop observing the content
+  // and forget everything.  Therefore, if it's not safe to send notification
+  // when script blocker is unlocked, we cannot send blur notification after
+  // that and before next focus notification.
+  // Anyway, as far as we know, IME doesn't try to query content when it loses
+  // focus.  So, this may not cause any problem.
+  mIMEHasFocus = false;
+  IMEStateManager::NotifyIME(IMENotification(NOTIFY_IME_OF_BLUR), widget);
+
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p   NotifyIMEOfBlur(), sent NOTIFY_IME_OF_BLUR", this));
+}
+
+void IMEContentObserver::UnregisterObservers() {
+  if (!mIsObserving) {
+    return;
+  }
+  mIsObserving = false;
+
+  if (mEditorBase) {
+    mEditorBase->SetIMEContentObserver(nullptr);
+  }
+
+  if (mSelection) {
+    mSelectionData.Clear();
+    mFocusedWidget = nullptr;
+  }
+
+  if (mRootElement) {
+    mRootElement->RemoveMutationObserver(this);
+  }
+
+  if (mDocumentObserver) {
+    RefPtr<DocumentObserver> documentObserver = mDocumentObserver;
+    documentObserver->StopObserving();
+  }
+
+  if (mDocShell) {
+    mDocShell->RemoveWeakScrollObserver(this);
+    mDocShell->RemoveWeakReflowObserver(this);
+  }
+}
+
+nsPresContext* IMEContentObserver::GetPresContext() const {
+  return mESM ? mESM->GetPresContext() : nullptr;
+}
+
+void IMEContentObserver::Destroy() {
+  // WARNING: When you change this method, you have to check Unlink() too.
+
+  // Note that don't send any notifications later from here.  I.e., notify
+  // IMEStateManager of the blur synchronously because IMEStateManager needs to
+  // stop notifying the main process if this is requested by the main process.
+  NotifyIMEOfBlur();
+  UnregisterObservers();
+  Clear();
+
+  mWidget = nullptr;
+  mIMENotificationRequests = nullptr;
+
+  if (mESM) {
+    mESM->OnStopObservingContent(this);
+    mESM = nullptr;
+  }
+}
+
+bool IMEContentObserver::Destroyed() const { return !mWidget; }
+
+void IMEContentObserver::DisconnectFromEventStateManager() { mESM = nullptr; }
+
+bool IMEContentObserver::MaybeReinitialize(nsIWidget& aWidget,
+                                           nsPresContext& aPresContext,
+                                           Element* aElement,
+                                           EditorBase& aEditorBase) {
+  if (!IsObservingContent(aPresContext, aElement)) {
+    return false;
+  }
+
+  if (GetState() == eState_StoppedObserving) {
+    Init(aWidget, aPresContext, aElement, aEditorBase);
+  }
+  return IsObserving(aPresContext, aElement);
+}
+
+bool IMEContentObserver::IsObserving(const nsPresContext& aPresContext,
+                                     const Element* aElement) const {
+  if (GetState() != eState_Observing) {
+    return false;
+  }
+  // If aElement is not a text control, aElement is an editing host or entire
+  // the document is editable in the design mode.  Therefore, return false if
+  // we're observing an anonymous subtree of a text control.
+  if (!aElement || !aElement->IsTextControlElement() ||
+      !static_cast<const TextControlElement*>(aElement)
+           ->IsSingleLineTextControlOrTextArea()) {
+    if (mIsTextControl) {
+      return false;
+    }
+  }
+  // If aElement is a text control, return true if we're observing the anonymous
+  // subtree of aElement.  Therefore, return false if we're observing with
+  // HTMLEditor.
+  else if (!mIsTextControl) {
+    return false;
+  }
+  return IsObservingContent(aPresContext, aElement);
+}
+
+bool IMEContentObserver::IsBeingInitializedFor(
+    const nsPresContext& aPresContext, const Element* aElement,
+    const EditorBase& aEditorBase) const {
+  return GetState() == eState_Initializing && mEditorBase == &aEditorBase &&
+         IsObservingContent(aPresContext, aElement);
+}
+
+bool IMEContentObserver::IsObserving(
+    const TextComposition& aTextComposition) const {
+  if (GetState() != eState_Observing) {
+    return false;
+  }
+  nsPresContext* const presContext = aTextComposition.GetPresContext();
+  if (NS_WARN_IF(!presContext)) {
+    return false;
+  }
+  if (presContext != GetPresContext()) {
+    return false;  // observing different document
+  }
+  auto* const elementHavingComposition =
+      Element::FromNodeOrNull(aTextComposition.GetEventTargetNode());
+  bool isObserving = IsObservingContent(*presContext, elementHavingComposition);
+#ifdef DEBUG
+  if (isObserving) {
+    if (mIsTextControl) {
+      MOZ_ASSERT(elementHavingComposition);
+      MOZ_ASSERT(elementHavingComposition->IsTextControlElement(),
+                 "Should've never started to observe non-text-control element");
+      // XXX Our fake focus move has not been implemented properly. So, the
+      // following assertions may fail, but I don't like to make the failures
+      // cause crash even in debug builds because it may block developers to
+      // debug web-compat issues.  On the other hand, it'd be nice if we can
+      // detect the bug with automated tests.  Therefore, the following
+      // assertions are NS_ASSERTION.
+      NS_ASSERTION(static_cast<TextControlElement*>(elementHavingComposition)
+                       ->IsSingleLineTextControlOrTextArea(),
+                   "Should've stopped observing when the type is changed");
+      NS_ASSERTION(!elementHavingComposition->IsInDesignMode(),
+                   "Should've stopped observing when the design mode started");
+    } else if (elementHavingComposition) {
+      NS_ASSERTION(
+          !elementHavingComposition->IsTextControlElement() ||
+              !static_cast<TextControlElement*>(elementHavingComposition)
+                   ->IsSingleLineTextControlOrTextArea(),
+          "Should've never started to observe text-control element or "
+          "stopped observing it when the type is changed");
+    } else {
+      MOZ_ASSERT(presContext->GetPresShell());
+      MOZ_ASSERT(presContext->GetPresShell()->GetDocument());
+      NS_ASSERTION(
+          presContext->GetPresShell()->GetDocument()->IsInDesignMode(),
+          "Should be observing entire the document only in the design mode");
+    }
+  }
+#endif  // #ifdef DEBUG
+  return isObserving;
+}
+
+IMEContentObserver::State IMEContentObserver::GetState() const {
+  if (!mSelection || !mRootElement || !mEditableNode) {
+    return eState_NotObserving;  // failed to initialize or finalized.
+  }
+  if (!mRootElement->IsInComposedDoc()) {
+    // the focused editor has already been reframed.
+    return eState_StoppedObserving;
+  }
+  return mIsObserving ? eState_Observing : eState_Initializing;
+}
+
+bool IMEContentObserver::IsObservingContent(const nsPresContext& aPresContext,
+                                            const Element* aElement) const {
+  return mEditableNode ==
+         IMEStateManager::GetRootEditableNode(aPresContext, aElement);
+}
+
+bool IMEContentObserver::IsEditorHandlingEventForComposition() const {
+  if (!mWidget) {
+    return false;
+  }
+  RefPtr<TextComposition> composition =
+      IMEStateManager::GetTextCompositionFor(mWidget);
+  if (!composition) {
+    return false;
+  }
+  return composition->IsEditorHandlingEvent();
+}
+
+bool IMEContentObserver::IsEditorComposing() const {
+  // Note that don't use TextComposition here. The important thing is,
+  // whether the editor already started to handle composition because
+  // web contents can change selection, text content and/or something from
+  // compositionstart event listener which is run before EditorBase handles it.
+  if (NS_WARN_IF(!mEditorBase)) {
+    return false;
+  }
+  return mEditorBase->IsIMEComposing();
+}
+
+nsresult IMEContentObserver::GetSelectionAndRoot(Selection** aSelection,
+                                                 Element** aRootElement) const {
+  if (!mEditableNode || !mSelection) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  NS_ASSERTION(mSelection && mRootElement, "uninitialized content observer");
+  NS_ADDREF(*aSelection = mSelection);
+  NS_ADDREF(*aRootElement = mRootElement);
+  return NS_OK;
+}
+
+void IMEContentObserver::OnSelectionChange(Selection& aSelection) {
+  if (!mIsObserving) {
+    return;
+  }
+
+  if (mWidget) {
+    bool causedByComposition = IsEditorHandlingEventForComposition();
+    bool causedBySelectionEvent = TextComposition::IsHandlingSelectionEvent();
+    bool duringComposition = IsEditorComposing();
+    MaybeNotifyIMEOfSelectionChange(causedByComposition, causedBySelectionEvent,
+                                    duringComposition);
+  }
+}
+
+void IMEContentObserver::ScrollPositionChanged() {
+  if (!NeedsPositionChangeNotification()) {
+    return;
+  }
+
+  MaybeNotifyIMEOfPositionChange();
+}
+
+NS_IMETHODIMP
+IMEContentObserver::Reflow(DOMHighResTimeStamp aStart,
+                           DOMHighResTimeStamp aEnd) {
+  if (!NeedsPositionChangeNotification()) {
+    return NS_OK;
+  }
+
+  MaybeNotifyIMEOfPositionChange();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+IMEContentObserver::ReflowInterruptible(DOMHighResTimeStamp aStart,
+                                        DOMHighResTimeStamp aEnd) {
+  if (!NeedsPositionChangeNotification()) {
+    return NS_OK;
+  }
+
+  MaybeNotifyIMEOfPositionChange();
+  return NS_OK;
+}
+
+nsresult IMEContentObserver::HandleQueryContentEvent(
+    WidgetQueryContentEvent* aEvent) {
+  // If the instance has normal selection cache and the query event queries
+  // normal selection's range, it should use the cached selection which was
+  // sent to the widget.  However, if this instance has already received new
+  // selection change notification but hasn't updated the cache yet (i.e.,
+  // not sending selection change notification to IME, don't use the cached
+  // value.  Note that don't update selection cache here since if you update
+  // selection cache here, IMENotificationSender won't notify IME of selection
+  // change because it looks like that the selection isn't actually changed.
+  const bool isSelectionCacheAvailable = aEvent->mUseNativeLineBreak &&
+                                         mSelectionData.IsInitialized() &&
+                                         !mNeedsToNotifyIMEOfSelectionChange;
+  if (isSelectionCacheAvailable && aEvent->mMessage == eQuerySelectedText &&
+      aEvent->mInput.mSelectionType == SelectionType::eNormal) {
+    aEvent->EmplaceReply();
+    if (mSelectionData.HasRange()) {
+      aEvent->mReply->mOffsetAndData.emplace(mSelectionData.mOffset,
+                                             mSelectionData.String(),
+                                             OffsetAndDataFor::SelectedString);
+      aEvent->mReply->mReversed = mSelectionData.mReversed;
+    }
+    aEvent->mReply->mContentsRoot = mRootElement;
+    aEvent->mReply->mWritingMode = mSelectionData.GetWritingMode();
+    // The selection cache in IMEContentObserver must always have been in
+    // an editing host (or an editable anonymous <div> element).  Therefore,
+    // we set mIsEditableContent to true here even though it's already been
+    // blurred or changed its editable state but the selection cache has not
+    // been invalidated yet.
+    aEvent->mReply->mIsEditableContent = true;
+    MOZ_LOG(sIMECOLog, LogLevel::Debug,
+            ("0x%p HandleQueryContentEvent(aEvent={ "
+             "mMessage=%s, mReply=%s })",
+             this, ToChar(aEvent->mMessage), ToString(aEvent->mReply).c_str()));
+    return NS_OK;
+  }
+
+  MOZ_LOG(sIMECOLog, LogLevel::Info,
+          ("0x%p HandleQueryContentEvent(aEvent={ mMessage=%s })", this,
+           ToChar(aEvent->mMessage)));
+
+  // If we can make the event's input offset absolute with TextComposition or
+  // mSelection, we should set it here for reducing the cost of computing
+  // selection start offset.  If ContentEventHandler receives a
+  // WidgetQueryContentEvent whose input offset is relative to insertion point,
+  // it computes current selection start offset (this may be expensive) and
+  // make the offset absolute value itself.
+  // Note that calling MakeOffsetAbsolute() makes the event a query event with
+  // absolute offset.  So, ContentEventHandler doesn't pay any additional cost
+  // after calling MakeOffsetAbsolute() here.
+  if (aEvent->mInput.mRelativeToInsertionPoint &&
+      aEvent->mInput.IsValidEventMessage(aEvent->mMessage)) {
+    RefPtr<TextComposition> composition =
+        IMEStateManager::GetTextCompositionFor(aEvent->mWidget);
+    if (composition) {
+      uint32_t compositionStart = composition->NativeOffsetOfStartComposition();
+      if (NS_WARN_IF(!aEvent->mInput.MakeOffsetAbsolute(compositionStart))) {
+        return NS_ERROR_FAILURE;
+      }
+    } else if (isSelectionCacheAvailable && mSelectionData.HasRange()) {
+      const uint32_t selectionStart = mSelectionData.mOffset;
+      if (NS_WARN_IF(!aEvent->mInput.MakeOffsetAbsolute(selectionStart))) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+  }
+
+  AutoRestore<bool> handling(mIsHandlingQueryContentEvent);
+  mIsHandlingQueryContentEvent = true;
+  ContentEventHandler handler(GetPresContext());
+  nsresult rv = handler.HandleQueryContentEvent(aEvent);
+  if (NS_WARN_IF(Destroyed())) {
+    // If this has already destroyed during querying the content, the query
+    // is outdated even if it's succeeded.  So, make the query fail.
+    aEvent->mReply.reset();
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   HandleQueryContentEvent(), WARNING, "
+             "IMEContentObserver has been destroyed during the query, "
+             "making the query fail",
+             this));
+    return rv;
+  }
+
+  if (aEvent->Succeeded() &&
+      NS_WARN_IF(aEvent->mReply->mContentsRoot != mRootElement)) {
+    // Focus has changed unexpectedly, so make the query fail.
+    aEvent->mReply.reset();
+  }
+  return rv;
+}
+
+nsresult IMEContentObserver::MaybeHandleSelectionEvent(
+    nsPresContext* aPresContext, WidgetSelectionEvent* aEvent) {
+  MOZ_ASSERT(aEvent);
+  MOZ_ASSERT(aEvent->mMessage == eSetSelection);
+  NS_ASSERTION(!mNeedsToNotifyIMEOfSelectionChange,
+               "Selection cache has not been updated yet");
+
+  MOZ_LOG(
+      sIMECOLog, LogLevel::Debug,
+      ("0x%p MaybeHandleSelectionEvent(aEvent={ "
+       "mMessage=%s, mOffset=%u, mLength=%u, mReversed=%s, "
+       "mExpandToClusterBoundary=%s, mUseNativeLineBreak=%s }), "
+       "mSelectionData=%s",
+       this, ToChar(aEvent->mMessage), aEvent->mOffset, aEvent->mLength,
+       ToChar(aEvent->mReversed), ToChar(aEvent->mExpandToClusterBoundary),
+       ToChar(aEvent->mUseNativeLineBreak), ToString(mSelectionData).c_str()));
+
+  // When we have Selection cache, and the caller wants to set same selection
+  // range, we shouldn't try to compute same range because it may be impossible
+  // if the range boundary is around element boundaries which won't be
+  // serialized with line breaks like close tags of inline elements.  In that
+  // case, inserting new text at different point may be different from intention
+  // of users or web apps which set current selection.
+  // FIXME: We cache only selection data computed with native line breaker
+  // lengths.  Perhaps, we should improve the struct to have both data of
+  // offset and length.  E.g., adding line break counts for both offset and
+  // length.
+  if (!mNeedsToNotifyIMEOfSelectionChange && aEvent->mUseNativeLineBreak &&
+      mSelectionData.IsInitialized() && mSelectionData.HasRange() &&
+      mSelectionData.StartOffset() == aEvent->mOffset &&
+      mSelectionData.Length() == aEvent->mLength) {
+    if (RefPtr<Selection> selection = mSelection) {
+      selection->ScrollIntoView(nsISelectionController::SELECTION_FOCUS_REGION,
+                                ScrollAxis(), ScrollAxis(), 0);
+    }
+    aEvent->mSucceeded = true;
+    return NS_OK;
+  }
+
+  ContentEventHandler handler(aPresContext);
+  return handler.OnSelectionEvent(aEvent);
+}
+
+bool IMEContentObserver::OnMouseButtonEvent(nsPresContext& aPresContext,
+                                            WidgetMouseEvent& aMouseEvent) {
+  if (!mIMENotificationRequests ||
+      !mIMENotificationRequests->WantMouseButtonEventOnChar()) {
+    return false;
+  }
+  if (!aMouseEvent.IsTrusted() || aMouseEvent.DefaultPrevented() ||
+      !aMouseEvent.mWidget) {
+    return false;
+  }
+  // Now, we need to notify only mouse down and mouse up event.
+  switch (aMouseEvent.mMessage) {
+    case eMouseUp:
+    case eMouseDown:
+      break;
+    default:
+      return false;
+  }
+  if (NS_WARN_IF(!mWidget) || NS_WARN_IF(mWidget->Destroyed())) {
+    return false;
+  }
+
+  WidgetQueryContentEvent queryCharAtPointEvent(true, eQueryCharacterAtPoint,
+                                                aMouseEvent.mWidget);
+  queryCharAtPointEvent.mRefPoint = aMouseEvent.mRefPoint;
+  ContentEventHandler handler(&aPresContext);
+  handler.OnQueryCharacterAtPoint(&queryCharAtPointEvent);
+  if (NS_WARN_IF(queryCharAtPointEvent.Failed()) ||
+      queryCharAtPointEvent.DidNotFindChar()) {
+    return false;
+  }
+
+  // The widget might be destroyed during querying the content since it
+  // causes flushing layout.
+  if (!mWidget || NS_WARN_IF(mWidget->Destroyed())) {
+    return false;
+  }
+
+  // The result character rect is relative to the top level widget.
+  // We should notify it with offset in the widget.
+  nsIWidget* topLevelWidget = mWidget->GetTopLevelWidget();
+  if (topLevelWidget && topLevelWidget != mWidget) {
+    queryCharAtPointEvent.mReply->mRect.MoveBy(
+        topLevelWidget->WidgetToScreenOffset() -
+        mWidget->WidgetToScreenOffset());
+  }
+  // The refPt is relative to its widget.
+  // We should notify it with offset in the widget.
+  if (aMouseEvent.mWidget != mWidget) {
+    queryCharAtPointEvent.mRefPoint +=
+        aMouseEvent.mWidget->WidgetToScreenOffset() -
+        mWidget->WidgetToScreenOffset();
+  }
+
+  IMENotification notification(NOTIFY_IME_OF_MOUSE_BUTTON_EVENT);
+  notification.mMouseButtonEventData.mEventMessage = aMouseEvent.mMessage;
+  notification.mMouseButtonEventData.mOffset =
+      queryCharAtPointEvent.mReply->StartOffset();
+  notification.mMouseButtonEventData.mCursorPos =
+      queryCharAtPointEvent.mRefPoint;
+  notification.mMouseButtonEventData.mCharRect =
+      queryCharAtPointEvent.mReply->mRect;
+  notification.mMouseButtonEventData.mButton = aMouseEvent.mButton;
+  notification.mMouseButtonEventData.mButtons = aMouseEvent.mButtons;
+  notification.mMouseButtonEventData.mModifiers = aMouseEvent.mModifiers;
+
+  nsresult rv = IMEStateManager::NotifyIME(notification, mWidget);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return false;
+  }
+
+  bool consumed = (rv == NS_SUCCESS_EVENT_CONSUMED);
+  if (consumed) {
+    aMouseEvent.PreventDefault();
+  }
+  return consumed;
+}
+
+void IMEContentObserver::CharacterDataWillChange(
+    nsIContent* aContent, const CharacterDataChangeInfo& aInfo) {
+  if (!aContent->IsText()) {
+    return;  // Ignore if it's a comment node or something other invisible data
+             // node.
+  }
+  MOZ_ASSERT(mPreCharacterDataChangeLength < 0,
+             "CharacterDataChanged() should've reset "
+             "mPreCharacterDataChangeLength");
+
+  if (!NeedsTextChangeNotification() ||
+      !nsContentUtils::IsInSameAnonymousTree(mRootElement, aContent)) {
+    return;
+  }
+
+  mEndOfAddedTextCache.Clear();
+  mStartOfRemovingTextRangeCache.Clear();
+
+  // Although we don't assume this change occurs while this is storing
+  // the range of added consecutive nodes, if it actually happens, we need to
+  // flush them since this change may occur before or in the range.  So, it's
+  // safe to flush pending computation of mTextChangeData before handling this.
+  MaybeNotifyIMEOfAddedTextDuringDocumentChange();
+
+  mPreCharacterDataChangeLength = ContentEventHandler::GetNativeTextLength(
+      *aContent->AsText(), aInfo.mChangeStart, aInfo.mChangeEnd);
+  MOZ_ASSERT(
+      mPreCharacterDataChangeLength >= aInfo.mChangeEnd - aInfo.mChangeStart,
+      "The computed length must be same as or larger than XP length");
+}
+
+void IMEContentObserver::CharacterDataChanged(
+    nsIContent* aContent, const CharacterDataChangeInfo& aInfo) {
+  if (!aContent->IsText()) {
+    return;  // Ignore if it's a comment node or something other invisible data
+             // node.
+  }
+
+  // Let TextComposition have a change to update composition string range in
+  // the text node if the change is caused by the web apps.
+  if (mWidget && !IsEditorHandlingEventForComposition()) {
+    if (RefPtr<TextComposition> composition =
+            IMEStateManager::GetTextCompositionFor(mWidget)) {
+      composition->OnCharacterDataChanged(*aContent->AsText(), aInfo);
+    }
+  }
+
+  if (!NeedsTextChangeNotification() ||
+      !nsContentUtils::IsInSameAnonymousTree(mRootElement, aContent)) {
+    return;
+  }
+
+  mEndOfAddedTextCache.Clear();
+  mStartOfRemovingTextRangeCache.Clear();
+  MOZ_ASSERT(
+      !HasAddedNodesDuringDocumentChange(),
+      "The stored range should be flushed before actually the data is changed");
+
+  int64_t removedLength = mPreCharacterDataChangeLength;
+  mPreCharacterDataChangeLength = -1;
+
+  MOZ_ASSERT(removedLength >= 0,
+             "mPreCharacterDataChangeLength should've been set by "
+             "CharacterDataWillChange()");
+
+  uint32_t offset = 0;
+  if (mIsTextControl) {
+    // If we're observing a text control, mRootElement is the anonymous <div>
+    // element which has only one text node and/or invisible <br> element.
+    // TextEditor assumes this structure when it handles editing commands.
+    // Therefore, it's safe to assume same things here.
+    MOZ_ASSERT(mRootElement->GetFirstChild() == aContent);
+    if (aInfo.mChangeStart) {
+      offset = ContentEventHandler::GetNativeTextLength(*aContent->AsText(), 0,
+                                                        aInfo.mChangeStart);
+    }
+  } else {
+    nsresult rv = ContentEventHandler::GetFlatTextLengthInRange(
+        RawNodePosition(mRootElement, 0u),
+        RawNodePosition(aContent, aInfo.mChangeStart), mRootElement, &offset,
+        LINE_BREAK_TYPE_NATIVE);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return;
+    }
+  }
+
+  uint32_t newLength = ContentEventHandler::GetNativeTextLength(
+      *aContent->AsText(), aInfo.mChangeStart,
+      aInfo.mChangeStart + aInfo.mReplaceLength);
+
+  uint32_t oldEnd = offset + static_cast<uint32_t>(removedLength);
+  uint32_t newEnd = offset + newLength;
+
+  TextChangeData data(offset, oldEnd, newEnd,
+                      IsEditorHandlingEventForComposition(),
+                      IsEditorComposing());
+  MaybeNotifyIMEOfTextChange(data);
+}
+
+void IMEContentObserver::NotifyContentAdded(nsINode* aContainer,
+                                            nsIContent* aFirstContent,
+                                            nsIContent* aLastContent) {
+  if (!NeedsTextChangeNotification() ||
+      !nsContentUtils::IsInSameAnonymousTree(mRootElement, aFirstContent)) {
+    return;
+  }
+
+  MOZ_ASSERT_IF(aFirstContent, aFirstContent->GetParentNode() == aContainer);
+  MOZ_ASSERT_IF(aLastContent, aLastContent->GetParentNode() == aContainer);
+
+  mStartOfRemovingTextRangeCache.Clear();
+
+  // If it's in a document change, nodes are added consecutively.  Therefore,
+  // if we cache the first node and the last node, we need to compute the
+  // range once.
+  // FYI: This is not true if the change caused by an operation in the editor.
+  if (IsInDocumentChange()) {
+    // Now, mEndOfAddedTextCache may be invalid if node is added before
+    // the last node in mEndOfAddedTextCache.  Clear it.
+    mEndOfAddedTextCache.Clear();
+    if (!HasAddedNodesDuringDocumentChange()) {
+      mFirstAddedContainer = mLastAddedContainer = aContainer;
+      mFirstAddedContent = aFirstContent;
+      mLastAddedContent = aLastContent;
+      MOZ_LOG(sIMECOLog, LogLevel::Debug,
+              ("0x%p   NotifyContentAdded(), starts to store consecutive added "
+               "nodes",
+               this));
+      return;
+    }
+    // If first node being added is not next node of the last node,
+    // notify IME of the previous range first, then, restart to cache the
+    // range.
+    if (NS_WARN_IF(!IsNextNodeOfLastAddedNode(aContainer, aFirstContent))) {
+      // Flush the old range first.
+      MaybeNotifyIMEOfAddedTextDuringDocumentChange();
+      mFirstAddedContainer = aContainer;
+      mFirstAddedContent = aFirstContent;
+      MOZ_LOG(sIMECOLog, LogLevel::Debug,
+              ("0x%p   NotifyContentAdded(), starts to store consecutive added "
+               "nodes",
+               this));
+    }
+    mLastAddedContainer = aContainer;
+    mLastAddedContent = aLastContent;
+    return;
+  }
+  MOZ_ASSERT(!HasAddedNodesDuringDocumentChange(),
+             "The cache should be cleared when document change finished");
+
+  uint32_t offset = 0;
+  nsresult rv = NS_OK;
+  if (!mEndOfAddedTextCache.Match(aContainer,
+                                  aFirstContent->GetPreviousSibling())) {
+    mEndOfAddedTextCache.Clear();
+    rv = ContentEventHandler::GetFlatTextLengthInRange(
+        RawNodePosition(mRootElement, 0u),
+        RawNodePositionBefore(aContainer,
+                              PointBefore(aContainer, aFirstContent)),
+        mRootElement, &offset, LINE_BREAK_TYPE_NATIVE);
+    if (NS_WARN_IF(NS_FAILED((rv)))) {
+      return;
+    }
+  } else {
+    offset = mEndOfAddedTextCache.mFlatTextLength;
+  }
+
+  // get offset at the end of the last added node
+  uint32_t addingLength = 0;
+  rv = ContentEventHandler::GetFlatTextLengthInRange(
+      RawNodePositionBefore(aContainer, PointBefore(aContainer, aFirstContent)),
+      RawNodePosition(aContainer, aLastContent), mRootElement, &addingLength,
+      LINE_BREAK_TYPE_NATIVE);
+  if (NS_WARN_IF(NS_FAILED((rv)))) {
+    mEndOfAddedTextCache.Clear();
+    return;
+  }
+
+  // If multiple lines are being inserted in an HTML editor, next call of
+  // NotifyContentAdded() is for adding next node.  Therefore, caching the text
+  // length can skip to compute the text length before the adding node and
+  // before of it.
+  mEndOfAddedTextCache.Cache(aContainer, aLastContent, offset + addingLength);
+
+  if (!addingLength) {
+    return;
+  }
+
+  TextChangeData data(offset, offset, offset + addingLength,
+                      IsEditorHandlingEventForComposition(),
+                      IsEditorComposing());
+  MaybeNotifyIMEOfTextChange(data);
+}
+
+void IMEContentObserver::ContentAppended(nsIContent* aFirstNewContent) {
+  nsIContent* parent = aFirstNewContent->GetParent();
+  MOZ_ASSERT(parent);
+  NotifyContentAdded(parent, aFirstNewContent, parent->GetLastChild());
+}
+
+void IMEContentObserver::ContentInserted(nsIContent* aChild) {
+  MOZ_ASSERT(aChild);
+  NotifyContentAdded(aChild->GetParentNode(), aChild, aChild);
+}
+
+void IMEContentObserver::ContentRemoved(nsIContent* aChild,
+                                        nsIContent* aPreviousSibling) {
+  if (!NeedsTextChangeNotification() ||
+      !nsContentUtils::IsInSameAnonymousTree(mRootElement, aChild)) {
+    return;
+  }
+
+  mEndOfAddedTextCache.Clear();
+  MaybeNotifyIMEOfAddedTextDuringDocumentChange();
+
+  nsINode* containerNode = aChild->GetParentNode();
+  MOZ_ASSERT(containerNode);
+
+  uint32_t offset = 0;
+  nsresult rv = NS_OK;
+  if (!mStartOfRemovingTextRangeCache.Match(containerNode, aPreviousSibling)) {
+    // At removing a child node of aContainer, we need the line break caused
+    // by open tag of aContainer.  Be careful when aPreviousSibling is nullptr.
+
+    rv = ContentEventHandler::GetFlatTextLengthInRange(
+        RawNodePosition(mRootElement, 0u),
+        RawNodePosition(containerNode, aPreviousSibling), mRootElement, &offset,
+        LINE_BREAK_TYPE_NATIVE);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mStartOfRemovingTextRangeCache.Clear();
+      return;
+    }
+    mStartOfRemovingTextRangeCache.Cache(containerNode, aPreviousSibling,
+                                         offset);
+  } else {
+    offset = mStartOfRemovingTextRangeCache.mFlatTextLength;
+  }
+
+  // get offset at the end of the deleted node
+  uint32_t textLength = 0;
+  if (const Text* textNode = Text::FromNode(aChild)) {
+    textLength = ContentEventHandler::GetNativeTextLength(*textNode);
+  } else {
+    nsresult rv = ContentEventHandler::GetFlatTextLengthInRange(
+        RawNodePositionBefore(aChild, 0u),
+        RawNodePosition(aChild, aChild->GetChildCount()), mRootElement,
+        &textLength, LINE_BREAK_TYPE_NATIVE, true);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mStartOfRemovingTextRangeCache.Clear();
+      return;
+    }
+  }
+
+  if (!textLength) {
+    return;
+  }
+
+  TextChangeData data(offset, offset + textLength, offset,
+                      IsEditorHandlingEventForComposition(),
+                      IsEditorComposing());
+  MaybeNotifyIMEOfTextChange(data);
+}
+
+void IMEContentObserver::ClearAddedNodesDuringDocumentChange() {
+  mFirstAddedContainer = mLastAddedContainer = nullptr;
+  mFirstAddedContent = mLastAddedContent = nullptr;
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p ClearAddedNodesDuringDocumentChange(), finished storing "
+           "consecutive nodes",
+           this));
+}
+
+bool IMEContentObserver::IsNextNodeOfLastAddedNode(nsINode* aParent,
+                                                   nsIContent* aChild) const {
+  MOZ_ASSERT(aParent);
+  MOZ_ASSERT(aChild && aChild->GetParentNode() == aParent);
+  MOZ_ASSERT(mRootElement);
+  MOZ_ASSERT(HasAddedNodesDuringDocumentChange());
+
+  // If the parent node isn't changed, we can check that mLastAddedContent has
+  // aChild as its next sibling.
+  if (aParent == mLastAddedContainer) {
+    return !NS_WARN_IF(mLastAddedContent->GetNextSibling() != aChild);
+  }
+
+  // If the parent node is changed, that means that the recorded last added node
+  // shouldn't have a sibling.
+  if (NS_WARN_IF(mLastAddedContent->GetNextSibling())) {
+    return false;
+  }
+
+  // If the node is aParent is a descendant of mLastAddedContainer,
+  // aChild should be the first child in the new container.
+  if (mLastAddedContainer == aParent->GetParent()) {
+    return !NS_WARN_IF(aChild->GetPreviousSibling());
+  }
+
+  // Otherwise, we need to check it even with slow path.
+  nsIContent* nextContentOfLastAddedContent =
+      mLastAddedContent->GetNextNode(mRootElement->GetParentNode());
+  if (NS_WARN_IF(!nextContentOfLastAddedContent)) {
+    return false;
+  }
+  if (NS_WARN_IF(nextContentOfLastAddedContent != aChild)) {
+    return false;
+  }
+  return true;
+}
+
+void IMEContentObserver::MaybeNotifyIMEOfAddedTextDuringDocumentChange() {
+  if (!HasAddedNodesDuringDocumentChange()) {
+    return;
+  }
+
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p "
+           "IMEContentObserver::MaybeNotifyIMEOfAddedTextDuringDocumentChange()"
+           ", flushing stored consecutive nodes",
+           this));
+
+  // Notify IME of text change which is caused by added nodes now.
+
+  // First, compute offset of start of first added node from start of the
+  // editor.
+  uint32_t offset;
+  nsresult rv = ContentEventHandler::GetFlatTextLengthInRange(
+      RawNodePosition(mRootElement, 0u),
+      RawNodePosition(mFirstAddedContainer,
+                      PointBefore(mFirstAddedContainer, mFirstAddedContent)),
+      mRootElement, &offset, LINE_BREAK_TYPE_NATIVE);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    ClearAddedNodesDuringDocumentChange();
+    return;
+  }
+
+  // Next, compute the text length of added nodes.
+  uint32_t length;
+  rv = ContentEventHandler::GetFlatTextLengthInRange(
+      RawNodePosition(mFirstAddedContainer,
+                      PointBefore(mFirstAddedContainer, mFirstAddedContent)),
+      RawNodePosition(mLastAddedContainer, mLastAddedContent), mRootElement,
+      &length, LINE_BREAK_TYPE_NATIVE);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    ClearAddedNodesDuringDocumentChange();
+    return;
+  }
+
+  // Finally, try to notify IME of the range.
+  TextChangeData data(offset, offset, offset + length,
+                      IsEditorHandlingEventForComposition(),
+                      IsEditorComposing());
+  MaybeNotifyIMEOfTextChange(data);
+  ClearAddedNodesDuringDocumentChange();
+}
+
+void IMEContentObserver::OnTextControlValueChangedWhileNotObservable(
+    const nsAString& aNewValue) {
+  MOZ_ASSERT(mEditorBase);
+  MOZ_ASSERT(mEditorBase->IsTextEditor());
+  if (!mTextControlValueLength && aNewValue.IsEmpty()) {
+    return;
+  }
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p OnTextControlValueChangedWhileNotObservable()", this));
+  uint32_t newLength = ContentEventHandler::GetNativeTextLength(aNewValue);
+  TextChangeData data(0, mTextControlValueLength, newLength, false, false);
+  MaybeNotifyIMEOfTextChange(data);
+}
+
+void IMEContentObserver::BeginDocumentUpdate() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p BeginDocumentUpdate(), HasAddedNodesDuringDocumentChange()=%s",
+           this, ToChar(HasAddedNodesDuringDocumentChange())));
+
+  // If we're not in a nested document update, this will return early,
+  // otherwise, it will handle flusing any changes currently pending before
+  // entering a nested document update.
+  MaybeNotifyIMEOfAddedTextDuringDocumentChange();
+}
+
+void IMEContentObserver::EndDocumentUpdate() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p EndDocumentUpdate(), HasAddedNodesDuringDocumentChange()=%s",
+           this, ToChar(HasAddedNodesDuringDocumentChange())));
+
+  MaybeNotifyIMEOfAddedTextDuringDocumentChange();
+}
+
+void IMEContentObserver::SuppressNotifyingIME() {
+  mSuppressNotifications++;
+
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p SuppressNotifyingIME(), mSuppressNotifications=%u", this,
+           mSuppressNotifications));
+}
+
+void IMEContentObserver::UnsuppressNotifyingIME() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p UnsuppressNotifyingIME(), mSuppressNotifications=%u", this,
+           mSuppressNotifications));
+
+  if (!mSuppressNotifications || --mSuppressNotifications) {
+    return;
+  }
+  FlushMergeableNotifications();
+}
+
+void IMEContentObserver::OnEditActionHandled() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug, ("0x%p EditAction()", this));
+
+  mEndOfAddedTextCache.Clear();
+  mStartOfRemovingTextRangeCache.Clear();
+  FlushMergeableNotifications();
+}
+
+void IMEContentObserver::BeforeEditAction() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug, ("0x%p BeforeEditAction()", this));
+
+  mEndOfAddedTextCache.Clear();
+  mStartOfRemovingTextRangeCache.Clear();
+}
+
+void IMEContentObserver::CancelEditAction() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug, ("0x%p CancelEditAction()", this));
+
+  mEndOfAddedTextCache.Clear();
+  mStartOfRemovingTextRangeCache.Clear();
+  FlushMergeableNotifications();
+}
+
+void IMEContentObserver::PostFocusSetNotification() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p PostFocusSetNotification()", this));
+
+  mNeedsToNotifyIMEOfFocusSet = true;
+}
+
+void IMEContentObserver::PostTextChangeNotification() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p PostTextChangeNotification(mTextChangeData=%s)", this,
+           ToString(mTextChangeData).c_str()));
+
+  MOZ_ASSERT(mTextChangeData.IsValid(),
+             "mTextChangeData must have text change data");
+  mNeedsToNotifyIMEOfTextChange = true;
+  // Even if the observer hasn't received selection change, selection in the
+  // flat text may have already been changed.  For example, when previous `<p>`
+  // element of another `<p>` element which contains caret is removed by a DOM
+  // mutation, selection change event won't be fired, but selection start offset
+  // should be decreased by the length of removed `<p>` element.
+  // In such case, HandleQueryContentEvent shouldn't use the selection cache
+  // anymore.  Therefore, we also need to post selection change notification
+  // too.  eQuerySelectedText event may be dispatched at sending a text change
+  // notification.
+  mNeedsToNotifyIMEOfSelectionChange = true;
+}
+
+void IMEContentObserver::PostSelectionChangeNotification() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p PostSelectionChangeNotification(), mSelectionData={ "
+           "mCausedByComposition=%s, mCausedBySelectionEvent=%s }",
+           this, ToChar(mSelectionData.mCausedByComposition),
+           ToChar(mSelectionData.mCausedBySelectionEvent)));
+
+  mNeedsToNotifyIMEOfSelectionChange = true;
+}
+
+void IMEContentObserver::MaybeNotifyIMEOfFocusSet() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p MaybeNotifyIMEOfFocusSet()", this));
+
+  PostFocusSetNotification();
+  FlushMergeableNotifications();
+}
+
+void IMEContentObserver::MaybeNotifyIMEOfTextChange(
+    const TextChangeDataBase& aTextChangeData) {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p MaybeNotifyIMEOfTextChange(aTextChangeData=%s)", this,
+           ToString(aTextChangeData).c_str()));
+
+  if (mEditorBase && mEditorBase->IsTextEditor()) {
+    MOZ_DIAGNOSTIC_ASSERT(static_cast<int64_t>(mTextControlValueLength) +
+                              aTextChangeData.Difference() >=
+                          0);
+    mTextControlValueLength += aTextChangeData.Difference();
+  }
+
+  mTextChangeData += aTextChangeData;
+  PostTextChangeNotification();
+  FlushMergeableNotifications();
+}
+
+void IMEContentObserver::CancelNotifyingIMEOfTextChange() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p CancelNotifyingIMEOfTextChange()", this));
+  mTextChangeData.Clear();
+  mNeedsToNotifyIMEOfTextChange = false;
+}
+
+void IMEContentObserver::MaybeNotifyIMEOfSelectionChange(
+    bool aCausedByComposition, bool aCausedBySelectionEvent,
+    bool aOccurredDuringComposition) {
+  MOZ_LOG(
+      sIMECOLog, LogLevel::Debug,
+      ("0x%p MaybeNotifyIMEOfSelectionChange(aCausedByComposition=%s, "
+       "aCausedBySelectionEvent=%s, aOccurredDuringComposition)",
+       this, ToChar(aCausedByComposition), ToChar(aCausedBySelectionEvent)));
+
+  mSelectionData.AssignReason(aCausedByComposition, aCausedBySelectionEvent,
+                              aOccurredDuringComposition);
+  PostSelectionChangeNotification();
+  FlushMergeableNotifications();
+}
+
+void IMEContentObserver::MaybeNotifyIMEOfPositionChange() {
+  MOZ_LOG(sIMECOLog, LogLevel::Verbose,
+          ("0x%p MaybeNotifyIMEOfPositionChange()", this));
+  // If reflow is caused by ContentEventHandler during PositionChangeEvent
+  // sending NOTIFY_IME_OF_POSITION_CHANGE, we don't need to notify IME of it
+  // again since ContentEventHandler returns the result including this reflow's
+  // result.
+  if (mIsHandlingQueryContentEvent &&
+      mSendingNotification == NOTIFY_IME_OF_POSITION_CHANGE) {
+    MOZ_LOG(sIMECOLog, LogLevel::Verbose,
+            ("0x%p   MaybeNotifyIMEOfPositionChange(), ignored since caused by "
+             "ContentEventHandler during sending NOTIFY_IME_OF_POSITION_CHANGE",
+             this));
+    return;
+  }
+  PostPositionChangeNotification();
+  FlushMergeableNotifications();
+}
+
+void IMEContentObserver::CancelNotifyingIMEOfPositionChange() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p CancelNotifyIMEOfPositionChange()", this));
+  mNeedsToNotifyIMEOfPositionChange = false;
+}
+
+void IMEContentObserver::MaybeNotifyCompositionEventHandled() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p MaybeNotifyCompositionEventHandled()", this));
+
+  PostCompositionEventHandledNotification();
+  FlushMergeableNotifications();
+}
+
+bool IMEContentObserver::UpdateSelectionCache(bool aRequireFlush /* = true */) {
+  MOZ_ASSERT(IsSafeToNotifyIME());
+
+  mSelectionData.ClearSelectionData();
+
+  // XXX Cannot we cache some information for reducing the cost to compute
+  //     selection offset and writing mode?
+  WidgetQueryContentEvent querySelectedTextEvent(true, eQuerySelectedText,
+                                                 mWidget);
+  querySelectedTextEvent.mNeedsToFlushLayout = aRequireFlush;
+  ContentEventHandler handler(GetPresContext());
+  handler.OnQuerySelectedText(&querySelectedTextEvent);
+  if (NS_WARN_IF(querySelectedTextEvent.Failed()) ||
+      NS_WARN_IF(querySelectedTextEvent.mReply->mContentsRoot !=
+                 mRootElement)) {
+    return false;
+  }
+
+  mFocusedWidget = querySelectedTextEvent.mReply->mFocusedWidget;
+  mSelectionData.Assign(querySelectedTextEvent);
+
+  // WARNING: Don't set the reason of selection change here because it should be
+  //          set the reason at sending the notification.
+
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p UpdateSelectionCache(), mSelectionData=%s", this,
+           ToString(mSelectionData).c_str()));
+
+  return true;
+}
+
+void IMEContentObserver::PostPositionChangeNotification() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p PostPositionChangeNotification()", this));
+
+  mNeedsToNotifyIMEOfPositionChange = true;
+}
+
+void IMEContentObserver::PostCompositionEventHandledNotification() {
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p PostCompositionEventHandledNotification()", this));
+
+  mNeedsToNotifyIMEOfCompositionEventHandled = true;
+}
+
+bool IMEContentObserver::IsReflowLocked() const {
+  nsPresContext* presContext = GetPresContext();
+  if (NS_WARN_IF(!presContext)) {
+    return false;
+  }
+  PresShell* presShell = presContext->GetPresShell();
+  if (NS_WARN_IF(!presShell)) {
+    return false;
+  }
+  // During reflow, we shouldn't notify IME because IME may query content
+  // synchronously.  Then, it causes ContentEventHandler will try to flush
+  // pending notifications during reflow.
+  return presShell->IsReflowLocked();
+}
+
+bool IMEContentObserver::IsSafeToNotifyIME() const {
+  // If this is already detached from the widget, this doesn't need to notify
+  // anything.
+  if (!mWidget) {
+    MOZ_LOG(sIMECOLog, LogLevel::Debug,
+            ("0x%p   IsSafeToNotifyIME(), it's not safe because of no widget",
+             this));
+    return false;
+  }
+
+  // Don't notify IME of anything if it's not good time to do it.
+  if (mSuppressNotifications) {
+    MOZ_LOG(sIMECOLog, LogLevel::Debug,
+            ("0x%p   IsSafeToNotifyIME(), it's not safe because of no widget",
+             this));
+    return false;
+  }
+
+  if (!mESM || NS_WARN_IF(!GetPresContext())) {
+    MOZ_LOG(sIMECOLog, LogLevel::Debug,
+            ("0x%p   IsSafeToNotifyIME(), it's not safe because of no "
+             "EventStateManager and/or PresContext",
+             this));
+    return false;
+  }
+
+  // If it's in reflow, we should wait to finish the reflow.
+  // FYI: This should be called again from Reflow() or ReflowInterruptible().
+  if (IsReflowLocked()) {
+    MOZ_LOG(
+        sIMECOLog, LogLevel::Debug,
+        ("0x%p   IsSafeToNotifyIME(), it's not safe because of reflow locked",
+         this));
+    return false;
+  }
+
+  // If we're in handling an edit action, this method will be called later.
+  if (mEditorBase && mEditorBase->IsInEditSubAction()) {
+    MOZ_LOG(sIMECOLog, LogLevel::Debug,
+            ("0x%p   IsSafeToNotifyIME(), it's not safe because of focused "
+             "editor handling somethings",
+             this));
+    return false;
+  }
+
+  return true;
+}
+
+void IMEContentObserver::FlushMergeableNotifications() {
+  if (!IsSafeToNotifyIME()) {
+    // So, if this is already called, this should do nothing.
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   FlushMergeableNotifications(), Warning, do nothing due to "
+             "unsafe to notify IME",
+             this));
+    return;
+  }
+
+  // Notifying something may cause nested call of this method.  For example,
+  // when somebody notified one of the notifications may dispatch query content
+  // event. Then, it causes flushing layout which may cause another layout
+  // change notification.
+
+  if (mQueuedSender) {
+    // So, if this is already called, this should do nothing.
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   FlushMergeableNotifications(), Warning, do nothing due to "
+             "already flushing pending notifications",
+             this));
+    return;
+  }
+
+  // If text change notification and/or position change notification becomes
+  // unnecessary, let's cancel them.
+  if (mNeedsToNotifyIMEOfTextChange && !NeedsTextChangeNotification()) {
+    CancelNotifyingIMEOfTextChange();
+  }
+  if (mNeedsToNotifyIMEOfPositionChange && !NeedsPositionChangeNotification()) {
+    CancelNotifyingIMEOfPositionChange();
+  }
+
+  if (!NeedsToNotifyIMEOfSomething()) {
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   FlushMergeableNotifications(), Warning, due to no pending "
+             "notifications",
+             this));
+    return;
+  }
+
+  // NOTE: Reset each pending flag because sending notification may cause
+  //       another change.
+
+  MOZ_LOG(
+      sIMECOLog, LogLevel::Info,
+      ("0x%p FlushMergeableNotifications(), creating IMENotificationSender...",
+       this));
+
+  // If contents in selection range is modified, the selection range still
+  // has removed node from the tree.  In such case, ContentIterator won't
+  // work well.  Therefore, we shouldn't use AddScriptRunner() here since
+  // it may kick runnable event immediately after DOM tree is changed but
+  // the selection range isn't modified yet.
+  mQueuedSender = new IMENotificationSender(this);
+  mQueuedSender->Dispatch(mDocShell);
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p   FlushMergeableNotifications(), finished", this));
+}
+
+void IMEContentObserver::TryToFlushPendingNotifications(bool aAllowAsync) {
+  // If a sender instance is sending notifications, we shouldn't try to create
+  // a new sender again because the sender will recreate by itself if there are
+  // new pending notifications.
+  if (mSendingNotification != NOTIFY_IME_OF_NOTHING) {
+    return;
+  }
+
+  // When the caller allows to put off notifying IME, we can wait the next
+  // call of this method or to run the queued sender.
+  if (mQueuedSender && XRE_IsContentProcess() && aAllowAsync) {
+    return;
+  }
+
+  if (!mQueuedSender) {
+    // If it was not safe to dispatch notifications when the pending
+    // notifications are posted, this may not have IMENotificationSender
+    // instance because it couldn't dispatch it, e.g., when an edit sub-action
+    // is being handled in the editor, we shouldn't do it even if it's safe to
+    // run script.  Therefore, we need to create the sender instance here in the
+    // case.
+    if (!NeedsToNotifyIMEOfSomething()) {
+      return;
+    }
+    mQueuedSender = new IMENotificationSender(this);
+  }
+
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p TryToFlushPendingNotifications(), performing queued "
+           "IMENotificationSender forcibly",
+           this));
+  RefPtr<IMENotificationSender> queuedSender = mQueuedSender;
+  queuedSender->Run();
+}
+
+/******************************************************************************
+ * mozilla::IMEContentObserver::AChangeEvent
+ ******************************************************************************/
+
+bool IMEContentObserver::AChangeEvent::CanNotifyIME(
+    ChangeEventType aChangeEventType) const {
+  RefPtr<IMEContentObserver> observer = GetObserver();
+  if (NS_WARN_IF(!observer)) {
+    return false;
+  }
+
+  const LogLevel debugOrVerbose =
+      aChangeEventType == ChangeEventType::eChangeEventType_Position
+          ? LogLevel::Verbose
+          : LogLevel::Debug;
+
+  if (aChangeEventType == eChangeEventType_CompositionEventHandled) {
+    if (observer->mWidget) {
+      return true;
+    }
+    MOZ_LOG(sIMECOLog, debugOrVerbose,
+            ("0x%p   AChangeEvent::CanNotifyIME(), Cannot notify IME of "
+             "composition event handled because of no widget",
+             this));
+    return false;
+  }
+  State state = observer->GetState();
+  // If it's not initialized, we should do nothing.
+  if (state == eState_NotObserving) {
+    MOZ_LOG(sIMECOLog, debugOrVerbose,
+            ("0x%p   AChangeEvent::CanNotifyIME(), Cannot notify IME because "
+             "of not observing",
+             this));
+    return false;
+  }
+  // If setting focus, just check the state.
+  if (aChangeEventType == eChangeEventType_Focus) {
+    if (!observer->mIMEHasFocus) {
+      return true;
+    }
+    MOZ_LOG(sIMECOLog, debugOrVerbose,
+            ("0x%p   AChangeEvent::CanNotifyIME(), Cannot notify IME of focus "
+             "change because of already focused",
+             this));
+    NS_WARNING("IME already has focus");
+    return false;
+  }
+  // If we've not notified IME of focus yet, we shouldn't notify anything.
+  if (!observer->mIMEHasFocus) {
+    MOZ_LOG(sIMECOLog, debugOrVerbose,
+            ("0x%p   AChangeEvent::CanNotifyIME(), Cannot notify IME because "
+             "of not focused",
+             this));
+    return false;
+  }
+
+  // If IME has focus, IMEContentObserver must hold the widget.
+  MOZ_ASSERT(observer->mWidget);
+
+  return true;
+}
+
+bool IMEContentObserver::AChangeEvent::IsSafeToNotifyIME(
+    ChangeEventType aChangeEventType) const {
+  const LogLevel warningOrVerbose =
+      aChangeEventType == ChangeEventType::eChangeEventType_Position
+          ? LogLevel::Verbose
+          : LogLevel::Warning;
+
+  if (NS_WARN_IF(!nsContentUtils::IsSafeToRunScript())) {
+    MOZ_LOG(sIMECOLog, warningOrVerbose,
+            ("0x%p   AChangeEvent::IsSafeToNotifyIME(), Warning, Cannot notify "
+             "IME because of not safe to run script",
+             this));
+    return false;
+  }
+
+  RefPtr<IMEContentObserver> observer = GetObserver();
+  if (!observer) {
+    MOZ_LOG(sIMECOLog, warningOrVerbose,
+            ("0x%p   AChangeEvent::IsSafeToNotifyIME(), Warning, Cannot notify "
+             "IME because of no observer",
+             this));
+    return false;
+  }
+
+  // While we're sending a notification, we shouldn't send another notification
+  // recursively.
+  if (observer->mSendingNotification != NOTIFY_IME_OF_NOTHING) {
+    MOZ_LOG(sIMECOLog, warningOrVerbose,
+            ("0x%p   AChangeEvent::IsSafeToNotifyIME(), Warning, Cannot notify "
+             "IME because of the observer sending another notification",
+             this));
+    return false;
+  }
+  State state = observer->GetState();
+  if (aChangeEventType == eChangeEventType_Focus) {
+    if (NS_WARN_IF(state != eState_Initializing && state != eState_Observing)) {
+      MOZ_LOG(sIMECOLog, warningOrVerbose,
+              ("0x%p   AChangeEvent::IsSafeToNotifyIME(), Warning, Cannot "
+               "notify IME of focus because of not observing",
+               this));
+      return false;
+    }
+  } else if (aChangeEventType == eChangeEventType_CompositionEventHandled) {
+    // It doesn't need to check the observing status.
+  } else if (state != eState_Observing) {
+    MOZ_LOG(sIMECOLog, warningOrVerbose,
+            ("0x%p   AChangeEvent::IsSafeToNotifyIME(), Warning, Cannot notify "
+             "IME because of not observing",
+             this));
+    return false;
+  }
+  return observer->IsSafeToNotifyIME();
+}
+
+/******************************************************************************
+ * mozilla::IMEContentObserver::IMENotificationSender
+ ******************************************************************************/
+
+void IMEContentObserver::IMENotificationSender::Dispatch(
+    nsIDocShell* aDocShell) {
+  if (XRE_IsContentProcess() && aDocShell) {
+    if (RefPtr<nsPresContext> presContext = aDocShell->GetPresContext()) {
+      if (nsRefreshDriver* refreshDriver = presContext->RefreshDriver()) {
+        refreshDriver->AddEarlyRunner(this);
+        return;
+      }
+    }
+  }
+  NS_DispatchToCurrentThread(this);
+}
+
+NS_IMETHODIMP
+IMEContentObserver::IMENotificationSender::Run() {
+  if (NS_WARN_IF(mIsRunning)) {
+    MOZ_LOG(
+        sIMECOLog, LogLevel::Error,
+        ("0x%p IMENotificationSender::Run(), FAILED, due to called recursively",
+         this));
+    return NS_OK;
+  }
+
+  RefPtr<IMEContentObserver> observer = GetObserver();
+  if (!observer) {
+    return NS_OK;
+  }
+
+  AutoRestore<bool> running(mIsRunning);
+  mIsRunning = true;
+
+  // This instance was already performed forcibly.
+  if (observer->mQueuedSender != this) {
+    return NS_OK;
+  }
+
+  // NOTE: Reset each pending flag because sending notification may cause
+  //       another change.
+
+  if (observer->mNeedsToNotifyIMEOfFocusSet) {
+    observer->mNeedsToNotifyIMEOfFocusSet = false;
+    SendFocusSet();
+    observer->mQueuedSender = nullptr;
+    // If it's not safe to notify IME of focus, SendFocusSet() sets
+    // mNeedsToNotifyIMEOfFocusSet true again.  For guaranteeing to send the
+    // focus notification later,  we should put a new sender into the queue but
+    // this case must be rare.  Note that if mIMEContentObserver is already
+    // destroyed, mNeedsToNotifyIMEOfFocusSet is never set true again.
+    if (observer->mNeedsToNotifyIMEOfFocusSet) {
+      MOZ_ASSERT(!observer->mIMEHasFocus);
+      MOZ_LOG(sIMECOLog, LogLevel::Debug,
+              ("0x%p IMENotificationSender::Run(), posting "
+               "IMENotificationSender to current thread",
+               this));
+      observer->mQueuedSender = new IMENotificationSender(observer);
+      observer->mQueuedSender->Dispatch(observer->mDocShell);
+      return NS_OK;
+    }
+    // This is the first notification to IME. So, we don't need to notify
+    // anymore since IME starts to query content after it gets focus.
+    observer->ClearPendingNotifications();
+    return NS_OK;
+  }
+
+  if (observer->mNeedsToNotifyIMEOfTextChange) {
+    observer->mNeedsToNotifyIMEOfTextChange = false;
+    SendTextChange();
+  }
+
+  // If a text change notification causes another text change again, we should
+  // notify IME of that before sending a selection change notification.
+  if (!observer->mNeedsToNotifyIMEOfTextChange) {
+    // Be aware, PuppetWidget depends on the order of this. A selection change
+    // notification should not be sent before a text change notification because
+    // PuppetWidget shouldn't query new text content every selection change.
+    if (observer->mNeedsToNotifyIMEOfSelectionChange) {
+      observer->mNeedsToNotifyIMEOfSelectionChange = false;
+      SendSelectionChange();
+    }
+  }
+
+  // If a text change notification causes another text change again or a
+  // selection change notification causes either a text change or another
+  // selection change, we should notify IME of those before sending a position
+  // change notification.
+  if (!observer->mNeedsToNotifyIMEOfTextChange &&
+      !observer->mNeedsToNotifyIMEOfSelectionChange) {
+    if (observer->mNeedsToNotifyIMEOfPositionChange) {
+      observer->mNeedsToNotifyIMEOfPositionChange = false;
+      SendPositionChange();
+    }
+  }
+
+  // Composition event handled notification should be sent after all the
+  // other notifications because this notifies widget of finishing all pending
+  // events are handled completely.
+  if (!observer->mNeedsToNotifyIMEOfTextChange &&
+      !observer->mNeedsToNotifyIMEOfSelectionChange &&
+      !observer->mNeedsToNotifyIMEOfPositionChange) {
+    if (observer->mNeedsToNotifyIMEOfCompositionEventHandled) {
+      observer->mNeedsToNotifyIMEOfCompositionEventHandled = false;
+      SendCompositionEventHandled();
+    }
+  }
+
+  observer->mQueuedSender = nullptr;
+
+  // If notifications caused some new change, we should notify them now.
+  if (observer->NeedsToNotifyIMEOfSomething()) {
+    if (observer->GetState() == eState_StoppedObserving) {
+      MOZ_LOG(sIMECOLog, LogLevel::Debug,
+              ("0x%p IMENotificationSender::Run(), waiting "
+               "IMENotificationSender to be reinitialized",
+               this));
+    } else {
+      MOZ_LOG(sIMECOLog, LogLevel::Debug,
+              ("0x%p IMENotificationSender::Run(), posting "
+               "IMENotificationSender to current thread",
+               this));
+      observer->mQueuedSender = new IMENotificationSender(observer);
+      observer->mQueuedSender->Dispatch(observer->mDocShell);
+    }
+  }
+  return NS_OK;
+}
+
+void IMEContentObserver::IMENotificationSender::SendFocusSet() {
+  RefPtr<IMEContentObserver> observer = GetObserver();
+  if (!observer) {
+    return;
+  }
+
+  if (!CanNotifyIME(eChangeEventType_Focus)) {
+    // If IMEContentObserver has already gone, we don't need to notify IME of
+    // focus.
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   IMENotificationSender::SendFocusSet(), Warning, does not "
+             "send notification due to impossible to notify IME of focus",
+             this));
+    observer->ClearPendingNotifications();
+    return;
+  }
+
+  if (!IsSafeToNotifyIME(eChangeEventType_Focus)) {
+    MOZ_LOG(
+        sIMECOLog, LogLevel::Warning,
+        ("0x%p   IMENotificationSender::SendFocusSet(), Warning, does not send "
+         "notification due to unsafe, retrying to send NOTIFY_IME_OF_FOCUS...",
+         this));
+    observer->PostFocusSetNotification();
+    return;
+  }
+
+  observer->mIMEHasFocus = true;
+  // Initialize selection cache with the first selection data.
+#ifdef XP_MACOSX
+  // We need to flush layout only on macOS because character coordinates are
+  // cached by cocoa with this call, but we don't have a way to update them
+  // after that.  Therefore, we need the latest layout information right now.
+  observer->UpdateSelectionCache(true);
+#else
+  // We avoid flushing for focus in the general case.
+  observer->UpdateSelectionCache(false);
+#endif  // #ifdef XP_MACOSX #else
+  MOZ_LOG(sIMECOLog, LogLevel::Info,
+          ("0x%p IMENotificationSender::SendFocusSet(), sending "
+           "NOTIFY_IME_OF_FOCUS...",
+           this));
+
+  MOZ_RELEASE_ASSERT(observer->mSendingNotification == NOTIFY_IME_OF_NOTHING);
+  observer->mSendingNotification = NOTIFY_IME_OF_FOCUS;
+  IMEStateManager::NotifyIME(IMENotification(NOTIFY_IME_OF_FOCUS),
+                             observer->mWidget);
+  observer->mSendingNotification = NOTIFY_IME_OF_NOTHING;
+
+  // IMENotificationRequests referred by ObserveEditableNode() may be different
+  // before or after widget receives NOTIFY_IME_OF_FOCUS.  Therefore, we need
+  // to guarantee to call ObserveEditableNode() after sending
+  // NOTIFY_IME_OF_FOCUS.
+  observer->OnIMEReceivedFocus();
+
+  MOZ_LOG(
+      sIMECOLog, LogLevel::Debug,
+      ("0x%p   IMENotificationSender::SendFocusSet(), sent NOTIFY_IME_OF_FOCUS",
+       this));
+}
+
+void IMEContentObserver::IMENotificationSender::SendSelectionChange() {
+  RefPtr<IMEContentObserver> observer = GetObserver();
+  if (!observer) {
+    return;
+  }
+
+  if (!CanNotifyIME(eChangeEventType_Selection)) {
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   IMENotificationSender::SendSelectionChange(), Warning, "
+             "does not send notification due to impossible to notify IME of "
+             "selection change",
+             this));
+    return;
+  }
+
+  if (!IsSafeToNotifyIME(eChangeEventType_Selection)) {
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   IMENotificationSender::SendSelectionChange(), Warning, "
+             "does not send notification due to unsafe, retrying to send "
+             "NOTIFY_IME_OF_SELECTION_CHANGE...",
+             this));
+    observer->PostSelectionChangeNotification();
+    return;
+  }
+
+  SelectionChangeData lastSelChangeData = observer->mSelectionData;
+  if (NS_WARN_IF(!observer->UpdateSelectionCache())) {
+    MOZ_LOG(sIMECOLog, LogLevel::Error,
+            ("0x%p   IMENotificationSender::SendSelectionChange(), FAILED, due "
+             "to UpdateSelectionCache() failure",
+             this));
+    return;
+  }
+
+  // The state may be changed since querying content causes flushing layout.
+  if (!CanNotifyIME(eChangeEventType_Selection)) {
+    MOZ_LOG(sIMECOLog, LogLevel::Error,
+            ("0x%p   IMENotificationSender::SendSelectionChange(), FAILED, due "
+             "to flushing layout having changed something",
+             this));
+    return;
+  }
+
+  // If the selection isn't changed actually, we shouldn't notify IME of
+  // selection change.
+  SelectionChangeData& newSelChangeData = observer->mSelectionData;
+  if (lastSelChangeData.IsInitialized() &&
+      lastSelChangeData.EqualsRangeAndDirectionAndWritingMode(
+          newSelChangeData)) {
+    MOZ_LOG(
+        sIMECOLog, LogLevel::Debug,
+        ("0x%p IMENotificationSender::SendSelectionChange(), not notifying IME "
+         "of NOTIFY_IME_OF_SELECTION_CHANGE due to not changed actually",
+         this));
+    return;
+  }
+
+  MOZ_LOG(sIMECOLog, LogLevel::Info,
+          ("0x%p IMENotificationSender::SendSelectionChange(), sending "
+           "NOTIFY_IME_OF_SELECTION_CHANGE... newSelChangeData=%s",
+           this, ToString(newSelChangeData).c_str()));
+
+  IMENotification notification(NOTIFY_IME_OF_SELECTION_CHANGE);
+  notification.SetData(observer->mSelectionData);
+
+  MOZ_RELEASE_ASSERT(observer->mSendingNotification == NOTIFY_IME_OF_NOTHING);
+  observer->mSendingNotification = NOTIFY_IME_OF_SELECTION_CHANGE;
+  IMEStateManager::NotifyIME(notification, observer->mWidget);
+  observer->mSendingNotification = NOTIFY_IME_OF_NOTHING;
+
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p   IMENotificationSender::SendSelectionChange(), sent "
+           "NOTIFY_IME_OF_SELECTION_CHANGE",
+           this));
+}
+
+void IMEContentObserver::IMENotificationSender::SendTextChange() {
+  RefPtr<IMEContentObserver> observer = GetObserver();
+  if (!observer) {
+    return;
+  }
+
+  if (!CanNotifyIME(eChangeEventType_Text)) {
+    MOZ_LOG(
+        sIMECOLog, LogLevel::Warning,
+        ("0x%p   IMENotificationSender::SendTextChange(), Warning, does not "
+         "send notification due to impossible to notify IME of text change",
+         this));
+    return;
+  }
+
+  if (!IsSafeToNotifyIME(eChangeEventType_Text)) {
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   IMENotificationSender::SendTextChange(), Warning, does "
+             "not send notification due to unsafe, retrying to send "
+             "NOTIFY_IME_OF_TEXT_CHANGE...",
+             this));
+    observer->PostTextChangeNotification();
+    return;
+  }
+
+  // If text change notification is unnecessary anymore, just cancel it.
+  if (!observer->NeedsTextChangeNotification()) {
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   IMENotificationSender::SendTextChange(), Warning, "
+             "canceling sending NOTIFY_IME_OF_TEXT_CHANGE",
+             this));
+    observer->CancelNotifyingIMEOfTextChange();
+    return;
+  }
+
+  MOZ_LOG(sIMECOLog, LogLevel::Info,
+          ("0x%p IMENotificationSender::SendTextChange(), sending "
+           "NOTIFY_IME_OF_TEXT_CHANGE... mIMEContentObserver={ "
+           "mTextChangeData=%s }",
+           this, ToString(observer->mTextChangeData).c_str()));
+
+  IMENotification notification(NOTIFY_IME_OF_TEXT_CHANGE);
+  notification.SetData(observer->mTextChangeData);
+  observer->mTextChangeData.Clear();
+
+  MOZ_RELEASE_ASSERT(observer->mSendingNotification == NOTIFY_IME_OF_NOTHING);
+  observer->mSendingNotification = NOTIFY_IME_OF_TEXT_CHANGE;
+  IMEStateManager::NotifyIME(notification, observer->mWidget);
+  observer->mSendingNotification = NOTIFY_IME_OF_NOTHING;
+
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p   IMENotificationSender::SendTextChange(), sent "
+           "NOTIFY_IME_OF_TEXT_CHANGE",
+           this));
+}
+
+void IMEContentObserver::IMENotificationSender::SendPositionChange() {
+  RefPtr<IMEContentObserver> observer = GetObserver();
+  if (!observer) {
+    return;
+  }
+
+  if (!CanNotifyIME(eChangeEventType_Position)) {
+    MOZ_LOG(sIMECOLog, LogLevel::Verbose,
+            ("0x%p   IMENotificationSender::SendPositionChange(), Warning, "
+             "does not send notification due to impossible to notify IME of "
+             "position change",
+             this));
+    return;
+  }
+
+  if (!IsSafeToNotifyIME(eChangeEventType_Position)) {
+    MOZ_LOG(sIMECOLog, LogLevel::Verbose,
+            ("0x%p   IMENotificationSender::SendPositionChange(), Warning, "
+             "does not send notification due to unsafe, retrying to send "
+             "NOTIFY_IME_OF_POSITION_CHANGE...",
+             this));
+    observer->PostPositionChangeNotification();
+    return;
+  }
+
+  // If position change notification is unnecessary anymore, just cancel it.
+  if (!observer->NeedsPositionChangeNotification()) {
+    MOZ_LOG(sIMECOLog, LogLevel::Verbose,
+            ("0x%p   IMENotificationSender::SendPositionChange(), Warning, "
+             "canceling sending NOTIFY_IME_OF_POSITION_CHANGE",
+             this));
+    observer->CancelNotifyingIMEOfPositionChange();
+    return;
+  }
+
+  MOZ_LOG(sIMECOLog, LogLevel::Info,
+          ("0x%p IMENotificationSender::SendPositionChange(), sending "
+           "NOTIFY_IME_OF_POSITION_CHANGE...",
+           this));
+
+  MOZ_RELEASE_ASSERT(observer->mSendingNotification == NOTIFY_IME_OF_NOTHING);
+  observer->mSendingNotification = NOTIFY_IME_OF_POSITION_CHANGE;
+  IMEStateManager::NotifyIME(IMENotification(NOTIFY_IME_OF_POSITION_CHANGE),
+                             observer->mWidget);
+  observer->mSendingNotification = NOTIFY_IME_OF_NOTHING;
+
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p   IMENotificationSender::SendPositionChange(), sent "
+           "NOTIFY_IME_OF_POSITION_CHANGE",
+           this));
+}
+
+void IMEContentObserver::IMENotificationSender::SendCompositionEventHandled() {
+  RefPtr<IMEContentObserver> observer = GetObserver();
+  if (!observer) {
+    return;
+  }
+
+  if (!CanNotifyIME(eChangeEventType_CompositionEventHandled)) {
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   IMENotificationSender::SendCompositionEventHandled(), "
+             "Warning, does not send notification due to impossible to notify "
+             "IME of composition event handled",
+             this));
+    return;
+  }
+
+  if (!IsSafeToNotifyIME(eChangeEventType_CompositionEventHandled)) {
+    MOZ_LOG(sIMECOLog, LogLevel::Warning,
+            ("0x%p   IMENotificationSender::SendCompositionEventHandled(), "
+             "Warning, does not send notification due to unsafe, retrying to "
+             "send NOTIFY_IME_OF_POSITION_CHANGE...",
+             this));
+    observer->PostCompositionEventHandledNotification();
+    return;
+  }
+
+  MOZ_LOG(sIMECOLog, LogLevel::Info,
+          ("0x%p IMENotificationSender::SendCompositionEventHandled(), sending "
+           "NOTIFY_IME_OF_COMPOSITION_EVENT_HANDLED...",
+           this));
+
+  MOZ_RELEASE_ASSERT(observer->mSendingNotification == NOTIFY_IME_OF_NOTHING);
+  observer->mSendingNotification = NOTIFY_IME_OF_COMPOSITION_EVENT_HANDLED;
+  IMEStateManager::NotifyIME(
+      IMENotification(NOTIFY_IME_OF_COMPOSITION_EVENT_HANDLED),
+      observer->mWidget);
+  observer->mSendingNotification = NOTIFY_IME_OF_NOTHING;
+
+  MOZ_LOG(sIMECOLog, LogLevel::Debug,
+          ("0x%p   IMENotificationSender::SendCompositionEventHandled(), sent "
+           "NOTIFY_IME_OF_COMPOSITION_EVENT_HANDLED",
+           this));
+}
+
+/******************************************************************************
+ * mozilla::IMEContentObserver::DocumentObservingHelper
+ ******************************************************************************/
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(IMEContentObserver::DocumentObserver)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(IMEContentObserver::DocumentObserver)
+  // StopObserving() releases mIMEContentObserver and mDocument.
+  tmp->StopObserving();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(IMEContentObserver::DocumentObserver)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mIMEContentObserver)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDocument)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(IMEContentObserver::DocumentObserver)
+  NS_INTERFACE_MAP_ENTRY(nsIDocumentObserver)
+  NS_INTERFACE_MAP_ENTRY(nsIMutationObserver)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(IMEContentObserver::DocumentObserver)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(IMEContentObserver::DocumentObserver)
+
+void IMEContentObserver::DocumentObserver::Observe(Document* aDocument) {
+  MOZ_ASSERT(aDocument);
+
+  // Guarantee that aDocument won't be destroyed during a call of
+  // StopObserving().
+  RefPtr<Document> newDocument = aDocument;
+
+  StopObserving();
+
+  mDocument = std::move(newDocument);
+  mDocument->AddObserver(this);
+}
+
+void IMEContentObserver::DocumentObserver::StopObserving() {
+  if (!IsObserving()) {
+    return;
+  }
+
+  // Grab IMEContentObserver which could be destroyed during method calls.
+  RefPtr<IMEContentObserver> observer = std::move(mIMEContentObserver);
+
+  // Stop observing the document first.
+  RefPtr<Document> document = std::move(mDocument);
+  document->RemoveObserver(this);
+
+  // Notify IMEContentObserver of ending of document updates if this already
+  // notified it of beginning of document updates.
+  for (; IsUpdating(); --mDocumentUpdating) {
+    // FYI: IsUpdating() returns true until mDocumentUpdating becomes 0.
+    //      However, IsObserving() returns false now because mDocument was
+    //      already cleared above.  Therefore, this method won't be called
+    //      recursively.
+    observer->EndDocumentUpdate();
+  }
+}
+
+void IMEContentObserver::DocumentObserver::Destroy() {
+  StopObserving();
+  mIMEContentObserver = nullptr;
+}
+
+void IMEContentObserver::DocumentObserver::BeginUpdate(Document* aDocument) {
+  if (NS_WARN_IF(Destroyed()) || NS_WARN_IF(!IsObserving())) {
+    return;
+  }
+  mDocumentUpdating++;
+  mIMEContentObserver->BeginDocumentUpdate();
+}
+
+void IMEContentObserver::DocumentObserver::EndUpdate(Document* aDocument) {
+  if (NS_WARN_IF(Destroyed()) || NS_WARN_IF(!IsObserving()) ||
+      NS_WARN_IF(!IsUpdating())) {
+    return;
+  }
+  mDocumentUpdating--;
+  mIMEContentObserver->EndDocumentUpdate();
+}
+
+}  // namespace mozilla