compositor worker: Use a WebThread for the compositor thread.

components/scheduler/child/child_scheduler.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 COMPONENTS_SCHEDULER_CHILD_CHILD_SCHEDULER_H_
 #define COMPONENTS_SCHEDULER_CHILD_CHILD_SCHEDULER_H_
 
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "components/scheduler/base/task_queue.h"
 #include "components/scheduler/child/single_thread_idle_task_runner.h"
 #include "components/scheduler/scheduler_export.h"
 
 namespace base {
 class MessageLoop;
 }
 
 namespace scheduler {
 
 class SCHEDULER_EXPORT ChildScheduler {
  public:
   virtual ~ChildScheduler() {}
 
   // Returns the default task runner.
-  // TODO(alexclarke): Change this to return a SingleThreadIdleTaskRunner.
-  virtual scoped_refptr<TaskQueue> DefaultTaskRunner() = 0;
+  virtual scoped_refptr<base::SingleThreadTaskRunner> DefaultTaskRunner() = 0;

[Sami, 2016/01/14 13:55:04]

Probably want to rebase this in top of your other patch?

[sadrul, 2016/01/14 15:20:40]

Yep, done.

 
   // Returns the idle task runner. Tasks posted to this runner may be reordered
   // relative to other task types and may be starved for an arbitrarily long
   // time if no idle time is available.
   virtual scoped_refptr<SingleThreadIdleTaskRunner> IdleTaskRunner() = 0;
 
   // Returns true if there is high priority work pending on the main thread
   // and the caller should yield to let the scheduler service that work. Note
   // that this is a stricter condition than |IsHighPriorityWorkAnticipated|,
   // restricted to the case where real work is pending.
@@ skipping 24 matching lines @@
   virtual void Shutdown() = 0;
 
  protected:
   ChildScheduler() {}
   DISALLOW_COPY_AND_ASSIGN(ChildScheduler);
 };
 
 }  // namespace scheduler
 
 #endif  // COMPONENTS_SCHEDULER_CHILD_CHILD_SCHEDULER_H_