Move most of the remaining users of WebContentsObserver::tab_contents() to use web_contents().

content/browser/renderer_host/render_view_host_delegate.cc

 // Copyright (c) 2011 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/browser/renderer_host/render_view_host_delegate.h"
 
 #include "googleurl/src/gurl.h"
 #include "webkit/glue/webpreferences.h"
 
+using content::WebContents;
+
 RenderViewHostDelegate::View* RenderViewHostDelegate::GetViewDelegate() {
   return NULL;
 }
 
 RenderViewHostDelegate::RendererManagement*
 RenderViewHostDelegate::GetRendererManagementDelegate() {
   return NULL;
 }
 
 bool RenderViewHostDelegate::OnMessageReceived(const IPC::Message& message) {
   return false;
 }
 
 const GURL& RenderViewHostDelegate::GetURL() const {
   return GURL::EmptyGURL();
 }
 
 TabContents* RenderViewHostDelegate::GetAsTabContents() {
   return NULL;
 }
 
+WebContents* RenderViewHostDelegate::GetAsWebContents() {
+  return NULL;
+}
+
 WebPreferences RenderViewHostDelegate::GetWebkitPrefs() {
   return WebPreferences();
 }
 
 bool RenderViewHostDelegate::PreHandleKeyboardEvent(
     const NativeWebKeyboardEvent& event, bool* is_keyboard_shortcut) {
   return false;
 }
 
 bool RenderViewHostDelegate::IsFullscreenForCurrentTab() const {
   return false;
 }