Get rid of redundant layout tree update related to selection

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

Index: third_party/WebKit/Source/core/editing/DOMSelection.cpp
diff --git a/third_party/WebKit/Source/core/editing/DOMSelection.cpp b/third_party/WebKit/Source/core/editing/DOMSelection.cpp
index 679549835d6f52797f6431e7053480efeaca286a..ae0fe16d111f7515328a25b561f49345225cd5fa 100644
--- a/third_party/WebKit/Source/core/editing/DOMSelection.cpp
+++ b/third_party/WebKit/Source/core/editing/DOMSelection.cpp
@@ -607,9 +607,7 @@ bool DOMSelection::containsNode(const Node* n, bool allowPartial) const {
   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();
@@ -619,8 +617,11 @@ bool DOMSelection::containsNode(const Node* n, bool allowPartial) const {
   // |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)