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

mojo/edk/util/waitable_event.h

 // Copyright 2015 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.
 
 // Provides classes with functionality analogous to (but much more limited than)
 // Chromium's |base::WaitableEvent|, which in turn provides functionality
 // analogous to Windows's Event. (Unlike these two, we have separate types for
 // the manual- and auto-reset versions.)
 
-#ifndef MOJO_EDK_SYSTEM_WAITABLE_EVENT_H_
-#define MOJO_EDK_SYSTEM_WAITABLE_EVENT_H_
+#ifndef MOJO_EDK_UTIL_WAITABLE_EVENT_H_
+#define MOJO_EDK_UTIL_WAITABLE_EVENT_H_
 
 #include "mojo/edk/util/cond_var.h"
 #include "mojo/edk/util/mutex.h"
 #include "mojo/edk/util/thread_annotations.h"
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
-namespace system {
+namespace util {
 
 // AutoResetWaitableEvent ------------------------------------------------------
 
 // An event that can be signaled and waited on. This version automatically
 // returns to the unsignaled state after unblocking one waiter. (This is similar
 // to Windows's auto-reset Event, which is also imitated by Chromium's
 // auto-reset |base::WaitableEvent|. However, there are some limitations -- see
 // |Signal()|.) This class is thread-safe.
 class AutoResetWaitableEvent {
  public:
@@ skipping 84 matching lines @@
   // waiting threads, one has to deal with spurious wake-ups. Checking
   // |signaled_| isn't sufficient, since another thread may have been awoken and
   // (manually) reset |signaled_|. This is a counter that is incremented in
   // |Signal()| before calling |CondVar::SignalAll()|. A waiting thread knows it
   // was awoken if |signal_id_| is different from when it started waiting.
   unsigned signal_id_ MOJO_GUARDED_BY(mutex_) = 0u;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(ManualResetWaitableEvent);
 };
 
-}  // namespace system
+}  // namespace util
 }  // namespace mojo
 
-#endif  // MOJO_EDK_SYSTEM_WAITABLE_EVENT_H_
+#endif  // MOJO_EDK_UTIL_WAITABLE_EVENT_H_