Changed EnabledRangeInRichlyEditableText() to use IsRichlyEditablePosition().

Changed EnabledRangeInRichlyEditableText() in Source/core/editing/
commands/EditorComand.cpp to use IsRichlyEditablePosition() instead of
VisibleSelection's IsContentRichlyEditable().

VisibleSelection: :IsContentRichlyEditable() to remove
Bug: 
Change-Id: Id808db032cbbb6d4bee01ed128b4bf57ae1dd78d
Reviewed-on: https://chromium-review.googlesource.com/627246
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496613}

third_party/WebKit/Source/core/editing/commands/EditorCommand.cpp

@@ -2212,7 +2212,7 @@ static bool EnabledRangeInRichlyEditableText(LocalFrame& frame,
     return false;
   const VisibleSelection& selection =
       frame.Selection().ComputeVisibleSelectionInDOMTree();
-  return selection.IsRange() && selection.IsContentRichlyEditable();
+  return selection.IsRange() && IsRichlyEditablePosition(selection.Base());
 }
 
 static bool EnabledRedo(LocalFrame& frame, Event*, EditorCommandSource) {