Fix devtools unable to start a shared workers.

content/public/browser/url_data_source.h

 // Copyright (c) 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_URL_DATA_SOURCE_H_
 #define CONTENT_PUBLIC_BROWSER_URL_DATA_SOURCE_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 36 matching lines @@
 
   // Used by StartDataRequest so that the child class can return the data when
   // it's available.
   typedef base::Callback<void(scoped_refptr<base::RefCountedMemory>)>
       GotDataCallback;
 
   // Called by URLDataSource to request data at |path|. The string parameter is
   // the path of the request. The child class should run |callback| when the
   // data is available or if the request could not be satisfied. This can be
   // called either in this callback or asynchronously with the response.
-  // |wc_getter| can be called to return the WebContents for this request, but
-  // only on the UI thread. If this method is called on the UI thread, then it's
-  // guaranteed that wc_getter will return a non-null WebContents.
+  // |wc_getter| can be called on the UI thread to return the WebContents for
+  // this request if it originates from a render frame. If it originated from a
+  // worker or if the frame has destructed it will return null.
   virtual void StartDataRequest(
       const std::string& path,
       const ResourceRequestInfo::WebContentsGetter& wc_getter,
       const GotDataCallback& callback) = 0;
 
   // Return the mimetype that should be sent with this response, or empty
   // string to specify no mime type.
   virtual std::string GetMimeType(const std::string& path) const = 0;
 
   // The following methods are all called on the IO thread.
@@ skipping 82 matching lines @@
       const net::URLRequest* request,
       std::string* path) const {}
 
   // Whether |path| is gzipped (and should be transmitted gzipped).
   virtual bool IsGzipped(const std::string& path) const;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_URL_DATA_SOURCE_H_