Added arrow key navigation to Overview Mode

ash/wm/overview/transparent_activate_window_button.cc

Index: ash/wm/overview/transparent_activate_window_button.cc
diff --git a/ash/wm/overview/transparent_activate_window_button.cc b/ash/wm/overview/transparent_activate_window_button.cc
index 216f0f33c326bc15ae4dd122861b7d89b9da3e07..a92e8bbf7d26271c90579ad418622ded36e931d3 100644
--- a/ash/wm/overview/transparent_activate_window_button.cc
+++ b/ash/wm/overview/transparent_activate_window_button.cc
@@ -53,7 +53,8 @@ TransparentActivateWindowButton::TransparentActivateWindowButton(
     aura::Window* activate_window)
     : event_handler_widget_(InitEventHandler(activate_window->GetRootWindow())),
       activate_window_(activate_window) {
-  views::View* transparent_button = new TransparentButton(this);
+  views::Button* transparent_button = new TransparentButton(this);
+  transparent_button->SetAccessibleName(activate_window->title());
   event_handler_widget_->SetContentsView(transparent_button);
 }
 
@@ -61,6 +62,11 @@ void TransparentActivateWindowButton::SetBounds(const gfx::Rect& bounds) {
   event_handler_widget_->SetBounds(bounds);
 }
 
+void TransparentActivateWindowButton::SendFocusAlert() const {
+  event_handler_widget_->GetContentsView()->
+      NotifyAccessibilityEvent(ui::AX_EVENT_FOCUS, true);
+}
+
 TransparentActivateWindowButton::~TransparentActivateWindowButton() {
 }