Re-implement form validation message UI with native widgets (GTK)

chrome/renderer/validation_message_agent.cc

 // Copyright (c) 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 "chrome/renderer/validation_message_agent.h"
 
 #include "base/i18n/rtl.h"
 #include "chrome/common/validation_message_messages.h"
 #include "content/public/renderer/render_view.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebView.h"
 
 ValidationMessageAgent::ValidationMessageAgent(content::RenderView* render_view)
     : content::RenderViewObserver(render_view)
 {
-#if defined(OS_MACOSX) || defined(TOOLKIT_VIEWS)
-  // TODO(tkent): enable this for other platforms.
-  // crbug.com/235717, crbug.com/235721.
+#if !defined(OS_ANDROID)
+  // TODO(tkent): enable this for Android. crbug.com/235721.
   render_view->GetWebView()->setValidationMessageClient(this);
 #endif
 }
 
 ValidationMessageAgent::~ValidationMessageAgent() {}
 
 void ValidationMessageAgent::showValidationMessage(
     const WebKit::WebRect& anchor_in_screen,
     const WebKit::WebString& main_text,
     const WebKit::WebString& sub_text,
@@ skipping 16 matching lines @@
   }
 
   Send(new ValidationMessageMsg_ShowValidationMessage(
       routing_id(), anchor_in_screen, wrapped_main_text, wrapped_sub_text));
 }
 
 void ValidationMessageAgent::hideValidationMessage() {
   Send(new ValidationMessageMsg_HideValidationMessage());
 }