Make FrameCaret to utilize SynchronousMutationObserver

third_party/WebKit/Source/core/editing/FrameSelection.cpp

Index: third_party/WebKit/Source/core/editing/FrameSelection.cpp
diff --git a/third_party/WebKit/Source/core/editing/FrameSelection.cpp b/third_party/WebKit/Source/core/editing/FrameSelection.cpp
index 0238e0b185480ab4010b2ce338dc56d0336b45ea..464ca351009703fc1146a4da0ce061f790eb36b5 100644
--- a/third_party/WebKit/Source/core/editing/FrameSelection.cpp
+++ b/third_party/WebKit/Source/core/editing/FrameSelection.cpp
@@ -403,8 +403,6 @@ void FrameSelection::nodeWillBeRemoved(Node& node) {
       removingNodeRemovesPosition(node, selection().extent()),
       removingNodeRemovesPosition(node, selection().start()),
       removingNodeRemovesPosition(node, selection().end()));
-
-  m_frameCaret->nodeWillBeRemoved(node);

[yoichio, 2017/01/20 08:44:00]

I'm afraid if there is race condition between  
FrameSelection::nodeWillBeRemoved and FrameCaret::nodeWillBeRemoved.

I think this kind of observer implementers should not depend on each
 other because order of nodeWilleBeRemoved call is not guaranteed.
respondToNodeModification calls m_Frame functions, is that O.K?

How about documentDetached listener?

[yosin_UTC9, 2017/01/20 08:49:14]

|FrameCaret::nodeWillBeRemoved()| doesn't access |FrameSelection| and there is
no back pointer to |FrameCaret| to |FrameSelection|. So, they are mutually
exclusive.

This is one of the requirements of utilizing SMO.
|SMO::contextDestroyed()| replaces |FrameCaret::documentDetached()|.
|documentDetached()| is an old protocol between |FrameSeleciton| and
|FrameCaret|.

 }
 
 static SelectionState selectionStateOf(const Node& node) {
@@ -711,6 +709,7 @@ void FrameSelection::documentAttached(Document* document) {
   m_document = document;
   m_useSecureKeyboardEntryWhenActive = false;
   m_selectionEditor->documentAttached(document);
+  m_frameCaret->documentAttached(document);
 }
 
 void FrameSelection::documentDetached(const Document& document) {
@@ -724,7 +723,6 @@ void FrameSelection::documentDetached(const Document& document) {
 
   clearTypingStyle();
   m_selectionEditor->documentDetached(document);
-  m_frameCaret->documentDetached();
 }
 
 LayoutBlock* FrameSelection::caretLayoutObject() const {