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

extensions/browser/guest_view/mime_handler_view/mime_handler_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/mime_handler_view/mime_handler_view_guest.h"
 
 #include "base/strings/stringprintf.h"
 #include "components/guest_view/common/guest_view_constants.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/navigation_entry.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/stream_handle.h"
 #include "content/public/browser/stream_info.h"
+#include "content/public/browser/web_contents_source.h"
 #include "content/public/common/service_registry.h"
 #include "content/public/common/url_constants.h"
 #include "extensions/browser/api/extensions_api_client.h"
 #include "extensions/browser/api/mime_handler_private/mime_handler_private.h"
 #include "extensions/browser/extension_registry.h"
 #include "extensions/browser/guest_view/mime_handler_view/mime_handler_stream_manager.h"
 #include "extensions/browser/guest_view/mime_handler_view/mime_handler_view_constants.h"
 #include "extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest_delegate.h"
 #include "extensions/browser/process_manager.h"
 #include "extensions/common/constants.h"
@@ skipping 100 matching lines @@
   // responsible for managing its own zoom. This is necessary for OOP PDF, as
   // otherwise the UI is zoomed and the calculations to determine the PDF size
   // mix zoomed and unzoomed units.
   content::HostZoomMap::Get(guest_site_instance.get())
       ->SetZoomLevelForHostAndScheme(kExtensionScheme, stream_->extension_id(),
                                      0);
 
   WebContents::CreateParams params(browser_context(),
                                    guest_site_instance.get());
   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 MimeHandlerViewGuest::DidAttachToEmbedder() {
   web_contents()->GetController().LoadURL(
       stream_->handler_url(), content::Referrer(),
       ui::PAGE_TRANSITION_AUTO_TOPLEVEL, std::string());
   web_contents()->GetMainFrame()->GetServiceRegistry()->AddService(
       base::Bind(&MimeHandlerServiceImpl::Create, stream_->GetWeakPtr()));
 }
 
@@ skipping 84 matching lines @@
           element_instance_id()));
 }
 
 base::WeakPtr<StreamContainer> MimeHandlerViewGuest::GetStream() const {
   if (!stream_)
     return base::WeakPtr<StreamContainer>();
   return stream_->GetWeakPtr();
 }
 
 }  // namespace extensions