Add OnDisplayMetricsChanged in DisplayObserver.

ash/wm/maximize_mode/maximize_mode_window_manager.cc

Index: ash/wm/maximize_mode/maximize_mode_window_manager.cc
diff --git a/ash/wm/maximize_mode/maximize_mode_window_manager.cc b/ash/wm/maximize_mode/maximize_mode_window_manager.cc
index 15d1ca2298bef42c37afa0a46fe1a97c931c7228..15278bfac23dede9f38991eed247418bdaaa9ee6 100644
--- a/ash/wm/maximize_mode/maximize_mode_window_manager.cc
+++ b/ash/wm/maximize_mode/maximize_mode_window_manager.cc
@@ -115,11 +115,6 @@ void MaximizeModeWindowManager::OnWindowBoundsChanged(
   }
 }
 
-void MaximizeModeWindowManager::OnDisplayBoundsChanged(
-    const gfx::Display& display) {
-  // Nothing to do here.
-}
-
 void MaximizeModeWindowManager::OnDisplayAdded(const gfx::Display& display) {
   DisplayConfigurationChanged();
 }
@@ -128,6 +123,11 @@ void MaximizeModeWindowManager::OnDisplayRemoved(const gfx::Display& display) {
   DisplayConfigurationChanged();
 }
 
+void MaximizeModeWindowManager::OnDisplayMetricsChanged(const gfx::Display&,
+                                                        uint32_t) {
+  // Nothing to do here.
+}
+
 void MaximizeModeWindowManager::OnTouchEvent(ui::TouchEvent* event) {
   if (event->type() != ui::ET_TOUCH_PRESSED)
     return;