chrome: Cleanup class/struct forward declarations

chrome/browser/net/chrome_url_request_context_getter.h

 // 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.
 
 #ifndef CHROME_BROWSER_NET_CHROME_URL_REQUEST_CONTEXT_GETTER_H_
 #define CHROME_BROWSER_NET_CHROME_URL_REQUEST_CONTEXT_GETTER_H_
 
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "chrome/browser/custom_handlers/protocol_handler_registry.h"
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "net/url_request/url_request_job_factory.h"
 
 class ChromeURLRequestContextFactory;
-class IOThread;
 class Profile;
 class ProfileIOData;
 struct StoragePartitionDescriptor;
 
 // A net::URLRequestContextGetter subclass used by the browser. This returns a
 // subclass of net::URLRequestContext which can be used to store extra
 // information about requests.
 //
 // Most methods are expected to be called on the UI thread, except for
 // the destructor and GetURLRequestContext().
@@ skipping 65 matching lines @@
   // NULL before initialization and after invalidation.
   // Otherwise, it is the URLRequestContext instance that
   // was lazily created by GetURLRequestContext().
   // Access only from the IO thread.
   net::URLRequestContext* url_request_context_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeURLRequestContextGetter);
 };
 
 #endif  // CHROME_BROWSER_NET_CHROME_URL_REQUEST_CONTEXT_GETTER_H_