Track where WebContents are created in order to better understand issue.

extensions/browser/guest_view/app_view/app_view_guest.cc

 // Copyright 2014 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 "extensions/browser/guest_view/app_view/app_view_guest.h"
 
 #include "base/command_line.h"
 #include "components/guest_view/browser/guest_view_manager.h"
 #include "content/public/browser/render_process_host.h"
+#include "content/public/browser/web_contents_source.h"
 #include "content/public/common/renderer_preferences.h"
 #include "extensions/browser/api/app_runtime/app_runtime_api.h"
 #include "extensions/browser/api/extensions_api_client.h"
 #include "extensions/browser/app_window/app_delegate.h"
 #include "extensions/browser/bad_message.h"
 #include "extensions/browser/event_router.h"
 #include "extensions/browser/extension_host.h"
 #include "extensions/browser/extension_registry.h"
 #include "extensions/browser/guest_view/app_view/app_view_constants.h"
 #include "extensions/browser/lazy_background_task_queue.h"
@@ skipping 222 matching lines @@
     return;
   }
   url_ = url;
   guest_extension_id_ = guest_extension->id();
 
   WebContents::CreateParams params(
       browser_context(),
       content::SiteInstance::CreateForURL(browser_context(),
                                           guest_extension->url()));
   params.guest_delegate = this;
-  callback.Run(WebContents::Create(params));
+  WebContents* web_contents = WebContents::Create(params);
+  WebContentsSource::CreateForWebContentsAndLocation(web_contents, FROM_HERE);
+  callback.Run(web_contents);
 }
 
 void AppViewGuest::LaunchAppAndFireEvent(
     scoped_ptr<base::DictionaryValue> data,
     const WebContentsCreatedCallback& callback,
     ExtensionHost* extension_host) {
   bool has_event_listener = EventRouter::Get(browser_context())
                                 ->ExtensionHasEventListener(
                                     extension_host->extension()->id(),
                                     app_runtime::OnEmbedRequested::kEventName);
@@ skipping 16 matching lines @@
 
 std::vector<int> AppViewGuest::GetAllRegisteredInstanceIdsForTesting() {
   std::vector<int> instances;
   for (const auto& key_value : pending_response_map.Get()) {
     instances.push_back(key_value.first);
   }
   return instances;
 }
 
 }  // namespace extensions