Aura-Mus: Allocate a LocalSurfaceId on size change

ui/aura/mus/window_mus.h

Index: ui/aura/mus/window_mus.h
diff --git a/ui/aura/mus/window_mus.h b/ui/aura/mus/window_mus.h
index c304dbceb731a22b9b7f92d8cad9605af81065c1..eb12493e6710baead86a19f2af9f0198a09888ba 100644
--- a/ui/aura/mus/window_mus.h
+++ b/ui/aura/mus/window_mus.h
@@ -76,7 +76,9 @@ class AURA_EXPORT WindowMus {
   virtual void ReorderFromServer(WindowMus* child,
                                  WindowMus* relative,
                                  ui::mojom::OrderDirection) = 0;
-  virtual void SetBoundsFromServer(const gfx::Rect& bounds) = 0;
+  virtual void SetBoundsFromServer(
+      const gfx::Rect& bounds,
+      const base::Optional<cc::LocalSurfaceId>& local_surface_id) = 0;
   virtual void SetVisibleFromServer(bool visible) = 0;
   virtual void SetOpacityFromServer(float opacity) = 0;
   virtual void SetPredefinedCursorFromServer(ui::mojom::CursorType cursor) = 0;
@@ -84,6 +86,8 @@ class AURA_EXPORT WindowMus {
                                      const std::vector<uint8_t>* data) = 0;
   virtual void SetFrameSinkIdFromServer(
       const cc::FrameSinkId& frame_sink_id) = 0;
+  virtual const cc::LocalSurfaceId& GetOrAllocateLocalSurfaceId(
+      const gfx::Size& new_size) = 0;
   virtual void SetSurfaceInfoFromServer(
       const cc::SurfaceInfo& surface_info) = 0;
   // The window was deleted on the server side. DestroyFromServer() should
@@ -95,6 +99,11 @@ class AURA_EXPORT WindowMus {
   virtual ChangeSource OnTransientChildAdded(WindowMus* child) = 0;
   virtual ChangeSource OnTransientChildRemoved(WindowMus* child) = 0;
 
+  // Returns the currently used cc::LocalSurfaceId to embed this Window. Local
+  // windows or windows that have not been embedded yet will have an invalid
+  // cc::LocalSurfaceId.
+  virtual const cc::LocalSurfaceId& GetLocalSurfaceId() = 0;
+
   // Called in the rare case when WindowTreeClient needs to change state and
   // can't go through one of the SetFooFromServer() functions above. Generally
   // because it needs to call another function that as a side effect changes the