Reland "EDK: Move //mojo/edk/system/waitable_event* to edk/util."

mojo/edk/system/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 MOJO_EDK_SYSTEM_TEST_TEST_IO_THREAD_H_
 #define MOJO_EDK_SYSTEM_TEST_TEST_IO_THREAD_H_
 
 #include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
 #include "base/task_runner.h"
@@ skipping 11 matching lines @@
   explicit TestIOThread(StartMode start_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.
   void Start();
   void Stop();
 
-  // Post |task| to the IO thread.
+  // Posts |task| to the I/O thread.
   void PostTask(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.
+  // Posts |task| to the I/O thread, blocking the calling thread until the
+  // posted task is executed (note the deadlock risk!).
   void PostTaskAndWait(const base::Closure& task);
 
   base::MessageLoopForIO* message_loop() {
     return static_cast<base::MessageLoopForIO*>(io_thread_.message_loop());
   }
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner() {
     return message_loop()->task_runner();
   }
 
  private:
   base::Thread io_thread_;
   bool io_thread_started_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(TestIOThread);
 };
 
 }  // namespace test
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_TEST_TEST_IO_THREAD_H_