Allow to have a transparent UA dependent background.

ui/views/controls/webview/webview.cc

 // Copyright (c) 2012 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 "ui/views/controls/webview/webview.h"
 
 #include <utility>
 
 #include "build/build_config.h"
 #include "content/public/browser/browser_accessibility_state.h"
@@ skipping 382 matching lines @@
 
   if (!contents) {
     content::WebContents::CreateParams create_params(
         browser_context, NULL);
     return content::WebContents::Create(create_params);
   }
 
   return contents;
 }
 
+void WebView::OnPaintBackground(gfx::Canvas* canvas) {
+  if (!GetWebContents()->GetRenderWidgetHostView()->GetBackgroundOpaque())
+    return;
+
+  View::OnPaintBackground(canvas);
+}
+
 }  // namespace views