aura: Move Window::ContainsMouse() implementation into the test API.

ui/aura/window.cc

Index: ui/aura/window.cc
diff --git a/ui/aura/window.cc b/ui/aura/window.cc
index fb25f62a3d24ed8e984851e5454033187a7baeb1..c4988e7beb6facbbdf890250fc7f20d11c300fb8 100644
--- a/ui/aura/window.cc
+++ b/ui/aura/window.cc
@@ -1443,16 +1443,6 @@ void Window::UpdateLayerName() {
 #endif
 }
 
-bool Window::ContainsMouse() {
-  bool contains_mouse = false;
-  if (IsVisible()) {
-    WindowTreeHost* host = GetHost();
-    contains_mouse = host &&
-        ContainsPointInRoot(host->dispatcher()->GetLastMouseLocationInRoot());
-  }
-  return contains_mouse;
-}
-
 const Window* Window::GetAncestorWithLayer(gfx::Vector2d* offset) const {
   for (const aura::Window* window = this; window; window = window->parent()) {
     if (window->layer())