Revert of ash/mash: Add a mus-client that sets up ash to provide the system ui for mash.

ui/base/user_activity/user_activity_detector.cc

 // Copyright 2014 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 "ui/base/user_activity/user_activity_detector.h"
 
 #include "base/format_macros.h"
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
 #include "build/build_config.h"
@@ skipping 35 matching lines @@
 // will be reported as user activity and turn the screen back on; too high
 // and we'll ignore legitimate activity.
 const int UserActivityDetector::kDisplayPowerChangeIgnoreMouseMs = 1000;
 
 UserActivityDetector::UserActivityDetector() {
   CHECK(!g_instance);
   g_instance = this;
 
   ui::PlatformEventSource* platform_event_source =
       ui::PlatformEventSource::GetInstance();
-  // TODO(sad): Need a PES for mus.
+#if defined(OS_CHROMEOS) || defined(OS_LINUX)
+  CHECK(platform_event_source);
+#endif
   if (platform_event_source)
     platform_event_source->AddPlatformEventObserver(this);
 }
 
 UserActivityDetector::~UserActivityDetector() {
   ui::PlatformEventSource* platform_event_source =
       ui::PlatformEventSource::GetInstance();
+#if defined(OS_CHROMEOS) || defined(OS_LINUX)
+  CHECK(platform_event_source);
+#endif
   if (platform_event_source)
     platform_event_source->RemovePlatformEventObserver(this);
   g_instance = nullptr;
 }
 
 // static
 UserActivityDetector* UserActivityDetector::Get() {
   return g_instance;
 }
 
@@ skipping 47 matching lines @@
       (now - last_observer_notification_time_).InMillisecondsF() >=
       kNotifyIntervalMs) {
     if (VLOG_IS_ON(1))
       VLOG(1) << "Reporting user activity: " << GetEventDebugString(event);
     FOR_EACH_OBSERVER(UserActivityObserver, observers_, OnUserActivity(event));
     last_observer_notification_time_ = now;
   }
 }
 
 }  // namespace ui