Move DisplayChangeObserver + tests from ash to ui.

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 82b55ed9f744535c7ec53c12b62fbd53090c6229..bc399ed69abd3c994a4838b24f4c774564a90997 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -119,7 +119,6 @@
 #include "ash/common/system/chromeos/bluetooth/bluetooth_notification_controller.h"
 #include "ash/common/system/chromeos/power/power_status.h"
 #include "ash/display/ash_display_string_provider.h"
-#include "ash/display/display_change_observer_chromeos.h"
 #include "ash/display/display_color_manager_chromeos.h"
 #include "ash/display/display_error_observer_chromeos.h"
 #include "ash/display/projecting_observer_chromeos.h"
@@ -137,6 +136,7 @@
 #include "chromeos/chromeos_switches.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "ui/chromeos/user_activity_power_manager_notifier.h"
+#include "ui/display/chromeos/display_change_observer.h"
 #include "ui/display/chromeos/display_configurator.h"
 
 #if defined(USE_X11)
@@ -623,11 +623,13 @@ void Shell::Init(const ShellInitParams& init_params) {
   wm_shell_->AddShellObserver(projecting_observer_.get());
 
   if (!display_initialized && base::SysInfo::IsRunningOnChromeOS()) {
-    display_change_observer_ = base::MakeUnique<DisplayChangeObserver>(
+    display_change_observer_ = base::MakeUnique<display::DisplayChangeObserver>(
         base::MakeUnique<AshDisplayStringProvider>());
     display_change_observer_->set_display_configurator(
         display_configurator_.get());
     display_change_observer_->set_display_manager(display_manager_.get());
+    display_change_observer_->set_display_changing_callback(
+        base::Bind(ui::UserActivityDetector::OnDisplayPowerChangingStatic));
 
     shutdown_observer_ =
         base::MakeUnique<ShutdownObserver>(display_configurator_.get());