make StackingClient dispatch to either ash or desktop

ui/aura/desktop/desktop_stacking_client.cc

Index: ui/aura/desktop/desktop_stacking_client.cc
diff --git a/ui/aura/desktop/desktop_stacking_client.cc b/ui/aura/desktop/desktop_stacking_client.cc
index 1ba464d137d878e458e88f19c4e25ec5314b3127..4409cd0acce12380926e716994c0e0d20607075e 100644
--- a/ui/aura/desktop/desktop_stacking_client.cc
+++ b/ui/aura/desktop/desktop_stacking_client.cc
@@ -17,7 +17,6 @@ namespace aura {
 
 DesktopStackingClient::DesktopStackingClient()
     : window_event_filter_(NULL) {
-  client::SetStackingClient(this);
 }
 
 DesktopStackingClient::~DesktopStackingClient() {
@@ -27,7 +26,8 @@ DesktopStackingClient::~DesktopStackingClient() {
   client::SetStackingClient(NULL);
 }
 
-Window* DesktopStackingClient::GetDefaultParent(Window* window,
+Window* DesktopStackingClient::GetDefaultParent(Window* context,
+                                                Window* window,
                                                 const gfx::Rect& bounds) {
   if (!null_parent_.get())
     CreateNULLParent();