Create content::WebContentsDestroyedWatcher, use it in many tests.

chrome/browser/apps/web_view_browsertest.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 "apps/native_app_window.h"
 #include "base/path_service.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/apps/app_browsertest_util.h"
 #include "chrome/browser/automation/automation_util.h"
@@ skipping 940 matching lines @@
                   embedder_web_contents,
                   "runTest('testRemoveWebviewOnExit')"));
   guest_observer.Wait();
 
   content::Source<content::NavigationController> source =
       guest_observer.source();
   EXPECT_TRUE(source->GetWebContents()->GetRenderProcessHost()->IsGuest());
 
   ASSERT_TRUE(guest_loaded_listener.WaitUntilSatisfied());
 
-  content::WindowedNotificationObserver observer(
-      content::NOTIFICATION_WEB_CONTENTS_DESTROYED,
-      content::Source<content::WebContents>(source->GetWebContents()));
+  content::WebContentsDestroyedWatcher destroyed_watcher(
+      source->GetWebContents());
 
   // Tell the embedder to kill the guest.
   EXPECT_TRUE(content::ExecuteScript(
                   embedder_web_contents,
                   "removeWebviewOnExitDoCrash();"));
 
   // Wait until the guest WebContents is destroyed.
-  observer.Wait();
+  destroyed_watcher.Wait();
 }
 
 // Remove <webview> immediately after navigating it.
 // This is a regression test for http://crbug.com/276023.
 IN_PROC_BROWSER_TEST_F(WebViewTest, Shim_TestRemoveWebviewAfterNavigation) {
   TestHelper("testRemoveWebviewAfterNavigation",
              "DoneShimTest.PASSED",
              "DoneShimTest.FAILED",
              "web_view/shim");
 }
@@ skipping 874 matching lines @@
   }
 };
 
 IN_PROC_BROWSER_TEST_F(WebViewPluginTest, TestLoadPluginEvent) {
   TestHelper("testPluginLoadPermission",
              "DoneShimTest.PASSED",
              "DoneShimTest.FAILED",
              "web_view/shim");
 }
 #endif  // defined(ENABLE_PLUGINS)