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

mojo/edk/system/channel_endpoint_unittest.cc

 // 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.
 
 #include "mojo/edk/system/channel_endpoint.h"
 
 #include <memory>
 #include <utility>
 
 #include "mojo/edk/system/channel_test_base.h"
 #include "mojo/edk/system/message_in_transit_queue.h"
 #include "mojo/edk/system/message_in_transit_test_utils.h"
 #include "mojo/edk/system/test/timeouts.h"
 #include "mojo/edk/system/test_channel_endpoint_client.h"
+#include "mojo/edk/system/waitable_event.h"
 #include "mojo/edk/util/ref_ptr.h"
-#include "mojo/edk/util/waitable_event.h"
 #include "mojo/public/cpp/system/macros.h"
 
 using mojo::util::MakeRefCounted;
-using mojo::util::ManualResetWaitableEvent;
 
 namespace mojo {
 namespace system {
 namespace {
 
 class ChannelEndpointTest : public test::ChannelTestBase {
  public:
   ChannelEndpointTest() {}
   ~ChannelEndpointTest() override {}
 
@@ skipping 98 matching lines @@
   for (unsigned message_id = 1; message_id <= 6; message_id++) {
     std::unique_ptr<MessageInTransit> read_message = client0->PopMessage();
     ASSERT_TRUE(read_message);
     test::VerifyTestMessage(read_message.get(), message_id);
   }
 }
 
 }  // namespace
 }  // namespace system
 }  // namespace mojo