Introduce TaskRunnerHandle.

base/threading/thread_task_runner_handle.h

Index: base/threading/thread_task_runner_handle.h
diff --git a/base/threading/thread_task_runner_handle.h b/base/threading/thread_task_runner_handle.h
index c8e58935f0977259349857bf91d71c63bf734567..7e389fb9a49df9ba6b607bd8da59e927960912a1 100644
--- a/base/threading/thread_task_runner_handle.h
+++ b/base/threading/thread_task_runner_handle.h
@@ -9,31 +9,34 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
+#include "base/threading/task_runner_handle.h"
 
 namespace base {
 
-// ThreadTaskRunnerHandle stores a reference to a thread's TaskRunner
-// in thread-local storage.  Callers can then retrieve the TaskRunner
-// for the current thread by calling ThreadTaskRunnerHandle::Get().
-// At most one TaskRunner may be bound to each thread at a time.
-// Prefer SequenceTaskRunnerHandle to this unless thread affinity is required.
+// Deprecated, see below for specifics.
 class BASE_EXPORT ThreadTaskRunnerHandle {
  public:
-  // Gets the SingleThreadTaskRunner for the current thread.
-  static scoped_refptr<SingleThreadTaskRunner> Get();
-
-  // Returns true if the SingleThreadTaskRunner is already created for
-  // the current thread.
-  static bool IsSet();
-
-  // Binds |task_runner| to the current thread. |task_runner| must belong
-  // to the current thread for this to succeed.
+  // Deprecated, use TaskRunnerHandle::Get.*() instead.
+  // Note: There will not be an automated ThreadTaskRunnerHandle::Get() =>
+  // TaskRunnerHandle::GetSingleThreaded() change. ThreadTaskRunnerHandle::Get()
+  // callsites should instead be examined one-by-one and given the right
+  // semantics for their use case (i.e. don't use GetSingleThreaded() unless
+  // truly thread-affine).
+  static scoped_refptr<SingleThreadTaskRunner> Get() {
+    return TaskRunnerHandle::GetSingleThreaded();
+  }
+
+  // Deprecated, use TaskRunnerHandle::HasSingleThreadTaskScope() instead.
+  static bool IsSet() { return TaskRunnerHandle::HasSingleThreadTaskScope(); }
+
+  // Binds |task_runner| to the current thread. Deprecated, use
+  // TaskRunnerHandle::SingleThreadTaskScope instead.
   explicit ThreadTaskRunnerHandle(
       scoped_refptr<SingleThreadTaskRunner> task_runner);
   ~ThreadTaskRunnerHandle();
 
  private:
-  scoped_refptr<SingleThreadTaskRunner> task_runner_;
+  TaskRunnerHandle::SingleThreadTaskScope task_scope_;
 
   DISALLOW_COPY_AND_ASSIGN(ThreadTaskRunnerHandle);
 };