Mark invariant member variables to const in ReplaceSelectionCommand

This patch add |const| to invariant member variables in
|ReplaceSelectionCommand| for improving readability.

Change-Id: I0ba290cbba3637145f09d948fc6a7ca926892453
Reviewed-on: https://chromium-review.googlesource.com/925879Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537751}

third_party/WebKit/Source/core/editing/commands/ReplaceSelectionCommand.h

@@ -145,14 +145,14 @@ class CORE_EXPORT ReplaceSelectionCommand final : public CompositeEditCommand {
   Position start_of_inserted_content_;
   Position end_of_inserted_content_;
   Member<EditingStyle> insertion_style_;
-  bool select_replacement_;
-  bool smart_replace_;
+  const bool select_replacement_;
+  const bool smart_replace_;
   bool match_style_;
   Member<DocumentFragment> document_fragment_;
   bool prevent_nesting_;
-  bool moving_paragraph_;
+  const bool moving_paragraph_;
   InputEvent::InputType input_type_;
-  bool sanitize_fragment_;
+  const bool sanitize_fragment_;
   bool should_merge_end_;
 
   Position start_of_inserted_range_;