ash: Add accelerator for snapping windows left/right.

ash/wm/window_util.cc

Index: ash/wm/window_util.cc
diff --git a/ash/wm/window_util.cc b/ash/wm/window_util.cc
index b273cb647801a767ba27f89e4aae0233c45e05c0..39fe454a316db5e4c18c8c1219cc1bb5896cdc6a 100644
--- a/ash/wm/window_util.cc
+++ b/ash/wm/window_util.cc
@@ -8,6 +8,9 @@
 #include "ash/wm/activation_controller.h"
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/aura_constants.h"
+#include "ui/aura/env.h"
+#include "ui/aura/monitor.h"
+#include "ui/aura/monitor_manager.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_property.h"
@@ -96,5 +99,13 @@ void RestoreWindow(aura::Window* window) {
   window->SetProperty(aura::client::kShowStateKey, ui::SHOW_STATE_NORMAL);
 }
 
+void CenterWindow(aura::Window* window) {
+  const aura::Monitor* monitor = aura::Env::GetInstance()->monitor_manager()->
+      GetMonitorNearestWindow(window);
+  gfx::Rect center = monitor->GetWorkAreaBounds().Center(
+      window->bounds().size());
+  window->SetBounds(center);
+}
+
 }  // namespace wm
 }  // namespace ash