Add base::ThreadTaskRunner class.

base/message_loop.h

Index: base/message_loop.h
diff --git a/base/message_loop.h b/base/message_loop.h
index c1ffc89f74d5a8d98ddb51253ca33a53f4354b7f..ef8d59f4071eac1d3785dba417f8b346503515d7 100644
--- a/base/message_loop.h
+++ b/base/message_loop.h
@@ -42,7 +42,8 @@
 
 namespace base {
 class Histogram;
-}
+class ThreadTaskRunnerHandle;
+}  // namespace base
 
 // A MessageLoop is used to process events for a particular thread.  There is
 // at most one MessageLoop instance per thread.
@@ -519,6 +520,7 @@ class BASE_EXPORT MessageLoop : public base::MessagePump::Delegate {
 
   // The message loop proxy associated with this message loop, if one exists.
   scoped_refptr<base::MessageLoopProxy> message_loop_proxy_;
+  scoped_ptr<base::ThreadTaskRunnerHandle> thread_task_runner_handle_;
 
  private:
   template <class T, class R> friend class base::subtle::DeleteHelperInternal;