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

chrome/browser/extensions/api/tab_capture/offscreen_tab.cc

 // Copyright 2015 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/extensions/api/tab_capture/offscreen_tab.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "chrome/browser/extensions/api/tab_capture/tab_capture_registry.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/web_contents_sizer.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_source.h"
 #include "extensions/browser/extension_host.h"
 #include "extensions/browser/process_manager.h"
 
 #if defined(USE_AURA)
 #include "base/memory/weak_ptr.h"
 #include "base/thread_task_runner_handle.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_list.h"
 #include "chrome/browser/ui/browser_window.h"
 #include "ui/aura/window.h"
@@ skipping 149 matching lines @@
                          const gfx::Size& initial_size,
                          const std::string& optional_presentation_id) {
   DCHECK(start_time_.is_null());
   start_url_ = start_url;
   DVLOG(1) << "Starting OffscreenTab with initial size of "
            << initial_size.ToString() << " for start_url=" << start_url_.spec();
 
   // Create the WebContents to contain the off-screen tab's page.
   offscreen_tab_web_contents_.reset(
       WebContents::Create(WebContents::CreateParams(profile_.get())));
+  WebContentsSource::CreateForWebContentsAndLocation(
+      offscreen_tab_web_contents_.get(), FROM_HERE);
   offscreen_tab_web_contents_->SetDelegate(this);
   WebContentsObserver::Observe(offscreen_tab_web_contents_.get());
 
 #if defined(USE_AURA)
   WindowAdoptionAgent::Start(offscreen_tab_web_contents_->GetNativeView());
 #endif
 
   // Set initial size, if specified.
   if (!initial_size.IsEmpty())
     ResizeWebContents(offscreen_tab_web_contents_.get(), initial_size);
@@ skipping 251 matching lines @@
 
   // Schedule the timer to check again in a second.
   capture_poll_timer_.Start(
       FROM_HERE,
       base::TimeDelta::FromSeconds(kPollIntervalInSeconds),
       base::Bind(&OffscreenTab::DieIfContentCaptureEnded,
                  base::Unretained(this)));
 }
 
 }  // namespace extensions