Desktop aura: Break aura::Window::SetParent in two.

ui/aura/client/stacking_client.h

Index: ui/aura/client/stacking_client.h
diff --git a/ui/aura/client/stacking_client.h b/ui/aura/client/stacking_client.h
index 023d8bf89a876781994b768d6f88de2b777b891c..6c0aa5973ffb51a259d7eac621b4cf083326a7c2 100644
--- a/ui/aura/client/stacking_client.h
+++ b/ui/aura/client/stacking_client.h
@@ -20,12 +20,15 @@ class AURA_EXPORT StackingClient {
  public:
   virtual ~StackingClient() {}
 
-  // Called by the Window when its parent is set to NULL, returns the window
-  // that |window| should be added to instead. |context| provides a Window
-  // (generally a RootWindow) that can be used to determine which desktop type
-  // the default parent should be chosen from.
-  // NOTE: this may have side effects. It should only be used when |window| is
-  // going to be immediately added.
+  // Called by the Window when it looks for a default parent. Returns the
+  // window that |window| should be added to instead. |context| provides a
+  // Window (generally a RootWindow) that can be used to determine which
+  // desktop type the default parent should be chosen from.  NOTE: this may
+  // have side effects. It should only be used when |window| is going to be
+  // immediately added.
+  //
+  // TODO(erg): Remove |context|, and maybe after oshima's patch lands,
+  // |bounds|.
   virtual Window* GetDefaultParent(
       Window* context,
       Window* window,
@@ -34,7 +37,7 @@ class AURA_EXPORT StackingClient {
 
 // Set/Get the default stacking client.
 AURA_EXPORT void SetStackingClient(StackingClient* stacking_client);
-AURA_EXPORT StackingClient* GetStackingClient();
+StackingClient* GetStackingClient();
 
 // Set/Get a stacking client for a specific window. Setting the stacking client
 // sets the stacking client on the window's RootWindow, not the window itself.
@@ -43,7 +46,7 @@ AURA_EXPORT StackingClient* GetStackingClient();
 // stacking client is used.
 AURA_EXPORT void SetStackingClient(Window* window,
                                    StackingClient* stacking_client);
-AURA_EXPORT StackingClient* GetStackingClient(Window* window);
+StackingClient* GetStackingClient(Window* window);
 
 }  // namespace client
 }  // namespace aura