[iOS] ios/web no longer depends on content::BrowserThread.

ios/web/public/web_thread.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 IOS_WEB_PUBLIC_WEB_THREAD_H_
 #define IOS_WEB_PUBLIC_WEB_THREAD_H_
 
 #include <string>
 
 #include "base/callback_forward.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/task_runner_util.h"
 
 namespace base {
 class MessageLoop;
 class SequencedWorkerPool;
 }
 
 namespace tracked_objects {
 class Location;
 }
 
 namespace web {
 
+class WebThreadDelegate;
+
 // Use DCHECK_CURRENTLY_ON_WEB_THREAD(WebThread::ID) to assert that a function
 // can only be called on the named WebThread.
 // TODO(ios): rename to DCHECK_CURRENTLY_ON once iOS is independent from
 // content/ so it won't collide with the macro DCHECK_CURRENTLY_ON in content/.
 // http://crbug.com/438202
 #define DCHECK_CURRENTLY_ON_WEB_THREAD(thread_identifier)   \
   (DCHECK(::web::WebThread::CurrentlyOn(thread_identifier)) \
    << ::web::WebThread::GetDCheckCurrentlyOnErrorMessage(thread_identifier))
 
 ///////////////////////////////////////////////////////////////////////////////
@@ skipping 161 matching lines @@
 
   // If the current message loop is one of the known threads, returns true and
   // sets identifier to its ID.
   static bool GetCurrentThreadIdentifier(ID* identifier) WARN_UNUSED_RESULT;
 
   // Callers can hold on to a refcounted SingleThreadTaskRunner beyond the
   // lifetime of the thread.
   static scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunnerForThread(
       ID identifier);
 
+  // Sets the delegate for the specified WebThread.
+  //
+  // Only one delegate may be registered at a time. Delegates may be
+  // unregistered by providing a nullptr pointer.
+  //
+  // If the caller unregisters a delegate before CleanUp has been
+  // called, it must perform its own locking to ensure the delegate is
+  // not deleted while unregistering.
+  static void SetDelegate(ID identifier, WebThreadDelegate* delegate);
+
   // Returns an appropriate error message for when
   // DCHECK_CURRENTLY_ON_WEB_THREAD() fails.
   static std::string GetDCheckCurrentlyOnErrorMessage(ID expected);
 
  private:
   friend class WebThreadImpl;
 
   WebThread() {}
   DISALLOW_COPY_AND_ASSIGN(WebThread);
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_WEB_THREAD_H_