Get rid of redundant layout tree update related to selection

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 589 matching lines @@
                    selectedRange->startContainer(),
                    selectedRange->startOffset(), ASSERT_NO_EXCEPTION);
 }
 
 bool DOMSelection::containsNode(const Node* n, bool allowPartial) const {
   DCHECK(n);
 
   if (!isAvailable())
     return false;
 
-  FrameSelection& selection = frame()->selection();
-
-  if (frame()->document() != n->document() || selection.isNone())

[yosin_UTC9, 2017/02/16 09:50:26]

FrameSeleciton::isNone() requires clean layout tree.
Rather than checking VisibleSelection::isNone() here,
checking whether |selectedRange| is null or not after
clean layout.

+  if (frame()->document() != n->document())
     return false;
 
   unsigned nodeIndex = n->nodeIndex();
 
   // TODO(xiaochengh): The use of updateStyleAndLayoutIgnorePendingStylesheets
   // needs to be audited.  See http://crbug.com/590369 for more details.
   // |VisibleSelection::toNormalizedEphemeralRange| requires clean layout.
   frame()->document()->updateStyleAndLayoutIgnorePendingStylesheets();
 
+  FrameSelection& selection = frame()->selection();
   const EphemeralRange selectedRange =
       selection.selection().toNormalizedEphemeralRange();
+  if (selectedRange.isNull())
+    return false;
 
   ContainerNode* parentNode = n->parentNode();
   if (!parentNode)
     return false;
 
   const Position startPosition =
       selectedRange.startPosition().toOffsetInAnchor();
   const Position endPosition = selectedRange.endPosition().toOffsetInAnchor();
   DummyExceptionStateForTesting exceptionState;
   bool nodeFullySelected =
@@ skipping 96 matching lines @@
     m_treeScope->document().addConsoleMessage(
         ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, message));
 }
 
 DEFINE_TRACE(DOMSelection) {
   visitor->trace(m_treeScope);
   ContextClient::trace(visitor);
 }
 
 }  // namespace blink