Added arrow key navigation to Overview Mode

ash/wm/overview/window_selector_item.cc

Index: ash/wm/overview/window_selector_item.cc
diff --git a/ash/wm/overview/window_selector_item.cc b/ash/wm/overview/window_selector_item.cc
index 77d06f39738585e7810bc30cbae5498f9f3d3941..762a772f5d4e797475301042ec6962f9853f8e3a 100644
--- a/ash/wm/overview/window_selector_item.cc
+++ b/ash/wm/overview/window_selector_item.cc
@@ -56,6 +56,8 @@ views::Widget* CreateWindowLabel(aura::Window* root_window,
   label->SetShadowColors(kLabelShadow, kLabelShadow);
   label->SetShadowOffset(0, kVerticalShadowOffset);
   label->set_shadow_blur(kShadowBlur);
+  // TODO(dmassoni): Change to something more appropriate.
+  label->set_accessible_role(ui::AX_ROLE_BUTTON);
   ui::ResourceBundle& bundle = ui::ResourceBundle::GetSharedInstance();
   label->SetFontList(bundle.GetFontList(ui::ResourceBundle::BoldFont));
   label->SetText(title);
@@ -154,7 +156,6 @@ void WindowSelectorItem::UpdateWindowLabels(const gfx::Rect& window_bounds,
       window_label_->GetNativeWindow()->SetBounds(label_bounds);
     }
   }
-
 }
 
 }  // namespace ash