aura-mus: Implement stacking in DesktopWindowTreeHostMus.

services/ui/ws/default_access_policy.cc

Index: services/ui/ws/default_access_policy.cc
diff --git a/services/ui/ws/default_access_policy.cc b/services/ui/ws/default_access_policy.cc
index 0acee434e1f5f47e05f9f8e971637d7386a2bbcd..9af1c07916cf46e611df840dafd7bd2a6f2eeec9 100644
--- a/services/ui/ws/default_access_policy.cc
+++ b/services/ui/ws/default_access_policy.cc
@@ -156,6 +156,10 @@ bool DefaultAccessPolicy::CanSetAcceptEvents(const ServerWindow* window) const {
          delegate_->HasRootForAccessPolicy(window);
 }
 
+bool DefaultAccessPolicy::CanStackAtTop(const ServerWindow* window) const {
+  return delegate_->HasRootForAccessPolicy(window);

[sky, 2017/01/20 16:36:10]

Can you also add a function to the delegate that checks if the window is owned
by the windowmanager, and check that too?

[Elliot Glaysher, 2017/01/20 22:31:02]

Done.

+}
+
 bool DefaultAccessPolicy::CanSetCursorProperties(
     const ServerWindow* window) const {
   return WasCreatedByThisClient(window) ||