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..4ad8dc9561aecc4a774d301ed11e9429c8fbfd4e 100644
--- a/ash/wm/window_util.cc
+++ b/ash/wm/window_util.cc
@@ -12,6 +12,7 @@
 #include "ui/aura/window.h"
 #include "ui/aura/window_property.h"
 #include "ui/base/ui_base_types.h"
+#include "ui/gfx/monitor.h"
 #include "ui/gfx/screen.h"
 
 DECLARE_WINDOW_PROPERTY_TYPE(bool);
@@ -96,5 +97,11 @@ void RestoreWindow(aura::Window* window) {
   window->SetProperty(aura::client::kShowStateKey, ui::SHOW_STATE_NORMAL);
 }
 
+void CenterWindow(aura::Window* window) {
+  const gfx::Monitor monitor = gfx::Screen::GetMonitorNearestWindow(window);
+  gfx::Rect center = monitor.work_area().Center(window->bounds().size());
+  window->SetBounds(center);
+}
+
 }  // namespace wm
 }  // namespace ash