Fix menu crash

 Made GetActivatableWindow to follow transient_parent if exists.

BUG=103820
TEST=tbd

Review URL: http://codereview.chromium.org/8523020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@109660 0039d316-1c4b-4281-b951-d872f2087c98

ui/aura_shell/stacking_controller.cc

@@ -42,6 +42,10 @@ aura::Window* StackingController::GetActivatableWindow(aura::Window* window) {
   while (parent) {
     if (SupportsChildActivation(parent))
       return child;
+    // If |child| isn't activatable, but has transient parent, trace
+    // that path instead.
+    if (child->transient_parent())
+      return GetActivatableWindow(child->transient_parent());
     parent = parent->parent();
     child = child->parent();
   }