Introduce Display Compositor mojo interface. Use InProcessContextProvider.

services/ui/ws/server_window_delegate.h

Index: services/ui/ws/server_window_delegate.h
diff --git a/services/ui/ws/server_window_delegate.h b/services/ui/ws/server_window_delegate.h
index affaa616cf53bda3205a66628fe12f6a3bcbf8e6..08db68fc1ded808bc7cac01f3f531d033a92c284 100644
--- a/services/ui/ws/server_window_delegate.h
+++ b/services/ui/ws/server_window_delegate.h
@@ -10,9 +10,14 @@
 #include "services/ui/public/interfaces/mus_constants.mojom.h"
 #include "services/ui/public/interfaces/window_tree.mojom.h"
 
+namespace cc {
+namespace mojom {
+class DisplayCompositor;
+}
+}
+
 namespace ui {
 
-class DisplayCompositor;
 
 namespace ws {
 
@@ -22,7 +27,9 @@ struct WindowId;
 
 class ServerWindowDelegate {
  public:
-  virtual DisplayCompositor* GetDisplayCompositor() = 0;
+  // Returns a display compositor interface pointer. There is only one
+  // DisplayCompositor running in the system.
+  virtual cc::mojom::DisplayCompositor* GetDisplayCompositor() = 0;
 
   // Returns the root of the window tree to which this |window| is attached.
   // Returns null if this window is not attached up through to a root window.