Revert of Add OnDisplayMetricsChanged in DisplayObserver.

ash/shell/window_watcher.cc

Index: ash/shell/window_watcher.cc
diff --git a/ash/shell/window_watcher.cc b/ash/shell/window_watcher.cc
index 44edaa4af64322d9cba7ca3b4692d9eca0f1dc08..55231cf7a0608148a22974e4fc43f7f635f64e4a 100644
--- a/ash/shell/window_watcher.cc
+++ b/ash/shell/window_watcher.cc
@@ -138,6 +138,9 @@
   }
 }
 
+void WindowWatcher::OnDisplayBoundsChanged(const gfx::Display& display) {
+}
+
 void WindowWatcher::OnDisplayAdded(const gfx::Display& new_display) {
   aura::Window* root = Shell::GetInstance()->display_controller()->
       GetRootWindowForDisplayId(new_display.id());
@@ -149,8 +152,5 @@
   // remove observers.
 }
 
-void WindowWatcher::OnDisplayMetricsChanged(const gfx::Display&, uint32_t) {
-}
-
 }  // namespace shell
 }  // namespace ash