Remove duplication between TestRunner's fields and LayoutDumpFlags struct.

content/shell/renderer/layout_test/layout_test_render_frame_observer.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/shell/renderer/layout_test/layout_test_render_frame_observer.h"
 
 #include <string>
 
 #include "components/test_runner/layout_dump.h"
 #include "components/test_runner/layout_dump_flags.h"
@@ skipping 22 matching lines @@
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(LayoutTestRenderFrameObserver, message)
     IPC_MESSAGE_HANDLER(ShellViewMsg_LayoutDumpRequest, OnLayoutDumpRequest)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
 
   return handled;
 }
 
 void LayoutTestRenderFrameObserver::OnLayoutDumpRequest(
-    test_runner::LayoutDumpFlags layout_dump_flags) {
+    const test_runner::LayoutDumpFlags& layout_dump_flags) {
   std::string dump =
       test_runner::DumpLayout(render_frame()->GetWebFrame(), layout_dump_flags);
   Send(new ShellViewHostMsg_LayoutDumpResponse(routing_id(), dump));
 }
 
 }  // namespace content