Support webview tag when the container extension is embedded in a webUI

chrome/renderer/extensions/document_custom_bindings.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 "chrome/renderer/extensions/document_custom_bindings.h"
 
 #include <string>
 
 #include "base/bind.h"
+#include "chrome/renderer/extensions/chrome_v8_context.h"
 #include "content/public/renderer/render_view.h"
 #include "third_party/WebKit/public/web/WebDocument.h"
 #include "third_party/WebKit/public/web/WebFrame.h"
 #include "third_party/WebKit/public/web/WebView.h"
 #include "v8/include/v8.h"
 
 namespace extensions {
 
 DocumentCustomBindings::DocumentCustomBindings(
     Dispatcher* dispatcher, ChromeV8Context* context)
@@ skipping 18 matching lines @@
 
   if (args.Length() != 2 || !args[0]->IsString() || !args[1]->IsObject()) {
     NOTREACHED();
     return;
   }
 
   std::string element_name(*v8::String::AsciiValue(args[0]));
   v8::Local<v8::Object> options = args[1]->ToObject();
 
   WebKit::WebExceptionCode ec = 0;
-  WebKit::WebDocument document = web_view->mainFrame()->document();
+  WebKit::WebDocument document = context()->web_frame()->document();
   v8::Handle<v8::Value> constructor =
       document.registerEmbedderCustomElement(
           WebKit::WebString::fromUTF8(element_name), options, ec);
   args.GetReturnValue().Set(constructor);
 }
 
 }  // namespace extensions