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

chrome/browser/plugin_observer.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 "chrome/browser/plugin_observer.h"
 
 #include "base/bind.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/content_settings/host_content_settings_map.h"
@@ skipping 334 matching lines @@
                  weak_ptr_factory_.GetWeakPtr(), installer)));
 }
 
 void PluginObserver::DidNotFindMissingPlugin(int placeholder_id,
                                              const std::string& mime_type) {
   Send(new ChromeViewMsg_DidNotFindMissingPlugin(placeholder_id));
 }
 
 void PluginObserver::InstallMissingPlugin(PluginInstaller* installer) {
   if (installer->url_for_display()) {
-    tab_contents()->OpenURL(OpenURLParams(
+    web_contents()->OpenURL(OpenURLParams(
         installer->plugin_url(),
-        content::Referrer(tab_contents()->GetURL(),
+        content::Referrer(web_contents()->GetURL(),
                           WebKit::WebReferrerPolicyDefault),
         NEW_FOREGROUND_TAB, content::PAGE_TRANSITION_TYPED, false));
   } else {
     NOTIMPLEMENTED();
   }
 }