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

content/public/browser/web_contents_source.h

+// 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.
+
+#ifndef CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_SOURCE_H_
+#define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_SOURCE_H_
+
+#include "base/location.h"
+#include "base/macros.h"
+#include "content/common/content_export.h"
+#include "content/public/browser/web_contents_user_data.h"
+
+class WebContentsSource
+    : public content::WebContentsUserData<WebContentsSource> {
+ public:
+  CONTENT_EXPORT static void CreateForWebContentsAndLocation(
+      content::WebContents* contents,
+      const tracked_objects::Location& created_location);
+
+  CONTENT_EXPORT tracked_objects::Location created_location() const {
+    return created_location_;
+  }
+
+ private:
+  explicit WebContentsSource(content::WebContents* contents);
+  friend class content::WebContentsUserData<WebContentsSource>;
+
+  tracked_objects::Location created_location_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebContentsSource);
+};
+
+#endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_SOURCE_H_