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

extensions/browser/app_window/app_window_contents.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 "extensions/browser/app_window/app_window_contents.h"
 
 #include <string>
 #include <utility>
 
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/resource_dispatcher_host.h"
 #include "content/public/browser/site_instance.h"
 #include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_source.h"
 #include "content/public/common/renderer_preferences.h"
 #include "extensions/browser/app_window/native_app_window.h"
 #include "extensions/common/extension_messages.h"
 
 namespace extensions {
 
 AppWindowContentsImpl::AppWindowContentsImpl(AppWindow* host)
     : host_(host), is_blocking_requests_(false), is_window_ready_(false) {}
 
 AppWindowContentsImpl::~AppWindowContentsImpl() {}
 
 void AppWindowContentsImpl::Initialize(content::BrowserContext* context,
                                        const GURL& url) {
   url_ = url;
 
   web_contents_.reset(
       content::WebContents::Create(content::WebContents::CreateParams(
           context, content::SiteInstance::CreateForURL(context, url_))));
+  WebContentsSource::CreateForWebContentsAndLocation(web_contents_.get(),
+                                                     FROM_HERE);
 
   Observe(web_contents_.get());
   web_contents_->GetMutableRendererPrefs()->
       browser_handles_all_top_level_requests = true;
   web_contents_->GetRenderViewHost()->SyncRendererPrefs();
 }
 
 void AppWindowContentsImpl::LoadContents(int32 creator_process_id) {
   // If the new view is in the same process as the creator, block the created
   // RVH from loading anything until the background page has had a chance to
@@ skipping 94 matching lines @@
   // TODO(devlin): This will need to change for site isolation.
   content::BrowserThread::PostTask(
       content::BrowserThread::IO, FROM_HERE,
       base::Bind(&content::ResourceDispatcherHost::BlockRequestsForRoute,
                  base::Unretained(content::ResourceDispatcherHost::Get()),
                  rfh->GetProcess()->GetID(),
                  rfh->GetRenderViewHost()->GetRoutingID()));
 }
 
 }  // namespace extensions