Add ScopedTaskEnvironment::GetMainThreadTaskRunner().

base/test/scoped_task_environment.h

Index: base/test/scoped_task_environment.h
diff --git a/base/test/scoped_task_environment.h b/base/test/scoped_task_environment.h
index fe7385ea477b14f9079568d52846a197308c5541..f46b516d7c16ddea6d7a6b710fd9a7832045dc29 100644
--- a/base/test/scoped_task_environment.h
+++ b/base/test/scoped_task_environment.h
@@ -7,6 +7,7 @@
 
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
+#include "base/single_thread_task_runner.h"
 
 namespace base {
 
@@ -67,6 +68,9 @@ class ScopedTaskEnvironment {
   // TaskScheduler and the (Thread|Sequenced)TaskRunnerHandle.
   ~ScopedTaskEnvironment();
 
+  // Returns a TaskRunner that schedules tasks on the main thread.
+  scoped_refptr<base::SingleThreadTaskRunner> GetMainThreadTaskRunner();
+
   // Synchronously runs (Thread|Sequenced)TaskRunnerHandle tasks until no
   // undelayed (Thread|Sequenced)TaskRunnerHandle or TaskScheduler tasks remain.
   void RunUntilIdle();