Implement aura::WindowPortMus::CreateCompositorFrameSink()

services/ui/public/interfaces/window_tree.mojom

Index: services/ui/public/interfaces/window_tree.mojom
diff --git a/services/ui/public/interfaces/window_tree.mojom b/services/ui/public/interfaces/window_tree.mojom
index 47c812cc250796164ad1aaa2d114650cb42fa949..0951c5a083ba58a3667223ae2c28ba83cc43f653 100644
--- a/services/ui/public/interfaces/window_tree.mojom
+++ b/services/ui/public/interfaces/window_tree.mojom
@@ -315,6 +315,10 @@ interface WindowTree {
   // Called by the client to cancel any in progress drag drop operation. This
   // will result in a change completed for the underlying change.
   CancelDragDrop(uint32 window_id);
+
+  // Get the FrameSinkId for the given window_id. The OnFrameSinkIdAllocated()
+  // will be called with the FrameSinkId.
+  GetFrameSinkId(uint32 window_id);
 };
 
 // Changes to windows are not sent to the connection that originated the
@@ -353,9 +357,9 @@ interface WindowTreeClient {
   // change.
   OnCaptureChanged(uint32 new_capture, uint32 old_capture);
 
-  // This is called on the owner of a window when it embeds a client in it,
-  // which includes the window manager creating a new window at the request of
-  // another client.
+  // This is called in response to GetFrameSinkId(), or on the owner of a window
+  // when it embeds a client in it, which includes the window manager creating
+  // a new window at the request of another client.
   OnFrameSinkIdAllocated(uint32 window, cc.mojom.FrameSinkId frame_sink_id);
 
   // Called in response to NewTopLevelWindow() successfully completing.