Selection API: Add a UseCounter for focus change by selection change.

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

 /*
  * Copyright (C) 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 64 matching lines @@
   return frame() && frame()->selection().isAvailable();
 }
 
 void DOMSelection::updateFrameSelection(const SelectionInDOMTree& selection,
                                         Range* newCachedRange) const {
   DCHECK(frame());
   FrameSelection& frameSelection = frame()->selection();
   // TODO(tkent): Specify FrameSelection::DoNotSetFocus. crbug.com/690272
   bool didSet = frameSelection.setSelectionDeprecated(selection);
   cacheRangeIfSelectionOfDocument(newCachedRange);
-  if (didSet)
-    frameSelection.didSetSelectionDeprecated();
+  if (!didSet)
+    return;
+  Element* focusedElement = frame()->document()->focusedElement();
+  frameSelection.didSetSelectionDeprecated();
+  if (focusedElement != frame()->document()->focusedElement())

[tkent, 2017/02/28 07:14:42]

This line crashed because frame() or frame()->document() can be null after focus
events.

+    UseCounter::count(frame(), UseCounter::SelectionFuncionsChangeFocus);
 }
 
 const VisibleSelection& DOMSelection::visibleSelection() const {
   DCHECK(frame());
   return frame()->selection().computeVisibleSelectionInDOMTreeDeprecated();
 }
 
 bool DOMSelection::isBaseFirstInSelection() const {
   DCHECK(frame());
   const SelectionInDOMTree& selection =
@@ skipping 728 matching lines @@
     m_treeScope->document().addConsoleMessage(
         ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, message));
 }
 
 DEFINE_TRACE(DOMSelection) {
   visitor->trace(m_treeScope);
   ContextClient::trace(visitor);
 }
 
 }  // namespace blink