Change Editor:CreateCommand to be const type.

This CL change Editor::CreateCommand to be const type for
improving code health.
Signed-off-by: Zhuoyu Qian <zhuoyu.qian@samsung.com>
Change-Id: I1e17c38f346d07f06cae0e736da0d550eacf3f74
Reviewed-on: https://chromium-review.googlesource.com/965723Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543998}

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

@@ -137,10 +137,9 @@ class CORE_EXPORT Editor final : public GarbageCollectedFinalized<Editor> {
     EditorCommandSource source_;
     Member<LocalFrame> frame_;
   };
-  Command CreateCommand(
-      const String&
-          command_name);  // Command source is CommandFromMenuOrKeyBinding.
-  Command CreateCommand(const String& command_name, EditorCommandSource);
+  Command CreateCommand(const String& command_name)
+      const;  // Command source is CommandFromMenuOrKeyBinding.
+  Command CreateCommand(const String& command_name, EditorCommandSource) const;
 
   // |Editor::executeCommand| is implementation of |WebFrame::executeCommand|
   // rather than |Document::execCommand|.

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

@@ -3466,13 +3466,13 @@ static const EditorInternalCommand* InternalCommand(
   return &kEditorCommands[command_index];
 }
 
-Editor::Command Editor::CreateCommand(const String& command_name) {
+Editor::Command Editor::CreateCommand(const String& command_name) const {
   return Command(InternalCommand(command_name),
                  EditorCommandSource::kMenuOrKeyBinding, frame_);
 }
 
 Editor::Command Editor::CreateCommand(const String& command_name,
-                                      EditorCommandSource source) {
+                                      EditorCommandSource source) const {
   return Command(InternalCommand(command_name), source, frame_);
 }