Introduce TaskRunnerHandle.

base/threading/sequenced_task_runner_handle.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 BASE_THREADING_SEQUENCED_TASK_RUNNER_HANDLE_H_
 #define BASE_THREADING_SEQUENCED_TASK_RUNNER_HANDLE_H_
 
-#include "base/compiler_specific.h"
+#include "base/base_export.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/sequenced_task_runner.h"
+#include "base/threading/task_runner_handle.h"
 
 namespace base {
 
+// Deprecated, see below for specifics.
+// TODO(gab): Migrate few users of this API and delete it.
 class BASE_EXPORT SequencedTaskRunnerHandle {
  public:
-  // Returns a SequencedTaskRunner which guarantees that posted tasks will only
-  // run after the current task is finished and will satisfy a SequenceChecker.
-  // It should only be called if IsSet() returns true (see the comment there for
-  // the requirements).
-  static scoped_refptr<SequencedTaskRunner> Get();
+  // Deprecated, use TaskRunnerHandle::GetSequenced() instead.
+  static scoped_refptr<SequencedTaskRunner> Get() {
+    return TaskRunnerHandle::GetSequenced();
+  }
 
-  // Returns true if one of the following conditions is fulfilled:
-  // a) A SequencedTaskRunner has been assigned to the current thread by
-  //    instantiating a SequencedTaskRunnerHandle.
-  // b) The current thread has a ThreadTaskRunnerHandle (which includes any
-  //    thread that has a MessageLoop associated with it), or
-  // c) The current thread is a worker thread belonging to a
-  //    SequencedWorkerPool.
-  static bool IsSet();
+  // Deprecated, use TaskRunnerHandle::HasSequencedTaskScope() instead.
+  static bool IsSet() { return TaskRunnerHandle::HasSequencedTaskScope(); }
 
-  // Binds |task_runner| to the current thread.
+  // Binds |task_runner| to the current thread. Deprecated, use
+  // TaskRunnerHandle::SequencedTaskScope instead.
   explicit SequencedTaskRunnerHandle(
       scoped_refptr<SequencedTaskRunner> task_runner);
   ~SequencedTaskRunnerHandle();
 
  private:
-  scoped_refptr<SequencedTaskRunner> task_runner_;
+  TaskRunnerHandle::SequencedTaskScope task_scope_;
 
   DISALLOW_COPY_AND_ASSIGN(SequencedTaskRunnerHandle);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_SEQUENCED_TASK_RUNNER_HANDLE_H_