Make new TaskRunner, SequencedTaskRunner, and SingleThreadTaskRunner interfaces

base/message_loop_proxy_impl.cc

Index: base/message_loop_proxy_impl.cc
diff --git a/base/message_loop_proxy_impl.cc b/base/message_loop_proxy_impl.cc
index e0ecd89ae016ed9e09fe02dd3068ed4c7e40d8b5..9740d67527aa267f661c988918da8c470e6460c7 100644
--- a/base/message_loop_proxy_impl.cc
+++ b/base/message_loop_proxy_impl.cc
@@ -36,7 +36,7 @@ bool MessageLoopProxyImpl::PostNonNestableDelayedTask(
   return PostTaskHelper(from_here, task, delay_ms, false);
 }
 
-bool MessageLoopProxyImpl::BelongsToCurrentThread() {
+bool MessageLoopProxyImpl::BelongsToCurrentThread() const {
   // We shouldn't use MessageLoop::current() since it uses LazyInstance which
   // may be deleted by ~AtExitManager when a WorkerPool thread calls this
   // function.