Add FlushForTesting to base::Thread.

base/threading/thread.h

 // Copyright (c) 2012 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 BASE_THREADING_THREAD_H_
 #define BASE_THREADING_THREAD_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 122 matching lines @@
   // WaitUntilThreadStarted().
   // Note that using this (instead of Start() or StartWithOptions() causes
   // jank on the calling thread, should be used only in testing code.
   bool StartAndWaitForTesting();
 
   // Blocks until the thread starts running. Called within StartAndWait().
   // Note that calling this causes jank on the calling thread, must be used
   // carefully for production code.
   bool WaitUntilThreadStarted() const;
 
+  // Blocks until all tasks previously posted to this thread have been executed.
+  void FlushForTesting();
+
   // Signals the thread to exit and returns once the thread has exited. The
   // Thread object is completely reset and may be used as if it were newly
   // constructed (i.e., Start may be called again). Can only be called if
   // |joinable_|.
   //
   // Stop may be called multiple times and is simply ignored if the thread is
   // already stopped or currently stopping.
   //
   // NOTE: If you are a consumer of Thread, it is not necessary to call this
   // before deleting your Thread objects, as the destructor will do it.
@@ skipping 153 matching lines @@
   // This class is not thread-safe, use this to verify access from the owning
   // sequence of the Thread.
   SequenceChecker owning_sequence_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_H_