Fix MemoryDumpManagerTest's thread unsafe usage of the base::TestIOThread API

base/test/test_io_thread.h

 // Copyright 2013 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_TEST_TEST_IO_THREAD_H_
 #define BASE_TEST_TEST_IO_THREAD_H_
 
 #include "base/callback_forward.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/task_runner.h"
 #include "base/threading/thread.h"
 #include "base/time/time.h"
 
 namespace base {
 
 // Create and run an IO thread with a MessageLoop, and
 // making the MessageLoop accessible from its client.
 // It also provides some ideomatic API like PostTaskAndWait().
+//
+// This API is not thread-safe:
+//   - Start()/Stop() should only be called from the main (creation) thread.
+//   - PostTask()/message_loop()/task_runner() are also safe to call from the
+//     underlying thread itself (to post tasks from other threads: get the
+//     task_runner() from the main thread first, it is then safe to pass _it_
+//     around).
 class TestIOThread {
  public:
   enum Mode { kAutoStart, kManualStart };
   explicit TestIOThread(Mode mode);
   // Stops the I/O thread if necessary.
   ~TestIOThread();
 
-  // |Start()|/|Stop()| should only be called from the main (creation) thread.
-  // After |Stop()|, |Start()| may be called again to start a new I/O thread.
-  // |Stop()| may be called even when the I/O thread is not started.
+  // After Stop(), Start() may be called again to start a new I/O thread.
+  // Stop() may be called even when the I/O thread is not started.
   void Start();
   void Stop();
 
   // Post |task| to the IO thread.
   void PostTask(const tracked_objects::Location& from_here,
                 const base::Closure& task);
-  // Posts |task| to the IO-thread with an WaitableEvent associated blocks on
-  // it until the posted |task| is executed, then returns.
-  void PostTaskAndWait(const tracked_objects::Location& from_here,
-                       const base::Closure& task);
 
   base::MessageLoopForIO* message_loop() {
     return static_cast<base::MessageLoopForIO*>(io_thread_.message_loop());
   }
 
   scoped_refptr<SingleThreadTaskRunner> task_runner() {
     return message_loop()->task_runner();
   }
 
  private:
   base::Thread io_thread_;
   bool io_thread_started_;
 
   DISALLOW_COPY_AND_ASSIGN(TestIOThread);
 };
 
 }  // namespace base
 
 #endif  // BASE_TEST_TEST_IO_THREAD_H_