Revert of Add OnDisplayMetricsChanged in DisplayObserver.

ash/shelf/shelf_window_watcher.cc

Index: ash/shelf/shelf_window_watcher.cc
diff --git a/ash/shelf/shelf_window_watcher.cc b/ash/shelf/shelf_window_watcher.cc
index 8cc31b6accc8052dbd895c730e041790c0007d3a..b16deeaf283c2265f703688079290a77db261c6b 100644
--- a/ash/shelf/shelf_window_watcher.cc
+++ b/ash/shelf/shelf_window_watcher.cc
@@ -267,6 +267,9 @@
   AddShelfItem(window);
 }
 
+void ShelfWindowWatcher::OnDisplayBoundsChanged(const gfx::Display& display) {
+}
+
 void ShelfWindowWatcher::OnDisplayAdded(const gfx::Display& new_display) {
   // Add a new RootWindow and its ActivationClient to observed list.
   aura::Window* root_window = Shell::GetInstance()->display_controller()->
@@ -285,8 +288,4 @@
   // Do nothing here.
 }
 
-void ShelfWindowWatcher::OnDisplayMetricsChanged(const gfx::Display&,
-                                                 uint32_t) {
-}
-
 }  // namespace ash