Add OnDisplayMetricsChanged in DisplayObserver.

ash/wm/overview/window_overview.cc

Index: ash/wm/overview/window_overview.cc
diff --git a/ash/wm/overview/window_overview.cc b/ash/wm/overview/window_overview.cc
index 640d21f2191b4507093cc47809b01a99634646ec..40b8b152e4ffd26c698587361170d22180bf08d8 100644
--- a/ash/wm/overview/window_overview.cc
+++ b/ash/wm/overview/window_overview.cc
@@ -307,16 +307,17 @@ void WindowOverview::OnTouchEvent(ui::TouchEvent* event) {
   window_selector_->SelectWindow(target);
 }
 
-void WindowOverview::OnDisplayBoundsChanged(const gfx::Display& display) {
-  PositionWindows(/* animate */ false);
-}
-
 void WindowOverview::OnDisplayAdded(const gfx::Display& display) {
 }
 
 void WindowOverview::OnDisplayRemoved(const gfx::Display& display) {
 }
 
+void WindowOverview::OnDisplayMetricsChanged(
+    const gfx::Display& display, gfx::DisplayObserver::MetricsType metrics) {
+  PositionWindows(/* animate */ false);
+}
+
 aura::Window* WindowOverview::GetEventTarget(ui::LocatedEvent* event) {
   aura::Window* target = static_cast<aura::Window*>(event->target());
   // If the target window doesn't actually contain the event location (i.e.