Changed Editor::CanEditRichly() to use IsRichlyEditablePosition().

Changed CanEditRichly() in Source/core/editing/Editor.cpp
to use IsRichlyEditablePosition() instead of
VisibleSelection::IsContentRichlyEditable() to remove
VisibleSelection's IsContentRichlyEditable().

Bug: 
Change-Id: Ib61170d6922ff8e2fbb667f7c56b7c22a144bd27
Reviewed-on: https://chromium-review.googlesource.com/627245
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496609}

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

@@ -294,10 +294,11 @@ bool Editor::CanEdit() const {
 }
 
 bool Editor::CanEditRichly() const {
-  return GetFrame()
-      .Selection()
-      .ComputeVisibleSelectionInDOMTreeDeprecated()
-      .IsContentRichlyEditable();
+  return IsRichlyEditablePosition(
+      GetFrame()
+          .Selection()
+          .ComputeVisibleSelectionInDOMTreeDeprecated()
+          .Base());
 }
 
 // WinIE uses onbeforecut and onbeforepaste to enables the cut and paste menu