Factor draw functionality out of DefaultPlatformDisplay into FrameGenerator.

components/mus/ws/frame_generator_delegate.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef COMPONENTS_MUS_WS_SERVER_WINDOW_TRACKER_H_
-#define COMPONENTS_MUS_WS_SERVER_WINDOW_TRACKER_H_
-
-#include <stdint.h>
-#include <set>
+#ifndef COMPONENTS_MUS_WS_FRAME_GENERATOR_DELEGATE_H_
+#define COMPONENTS_MUS_WS_FRAME_GENERATOR_DELEGATE_H_
 
 #include "base/macros.h"
-#include "components/mus/ws/server_window.h"
-#include "components/mus/ws/server_window_observer.h"
-#include "ui/base/window_tracker_template.h"
 
 namespace mus {
 namespace ws {
 
-using ServerWindowTracker =
-    ui::WindowTrackerTemplate<ServerWindow, ServerWindowObserver>;
+class ServerWindow;
+
+struct ViewportMetrics {
+  gfx::Size size_in_pixels;
+  float device_scale_factor = 0.f;
+};
+
+class FrameGeneratorDelegate {
+ public:
+  virtual ~FrameGeneratorDelegate(){};

[sky, 2016/06/30 23:40:20]

nit: no ';', space after '()' and move to protected section.

[mfomitchev, 2016/07/06 15:53:09]

Done.

+
+  // Returns the root window of the display.
+  virtual ServerWindow* GetRootWindow() = 0;
+
+  // Called when a compositor frame is finished drawing.
+  virtual void OnCompositorFrameDrawn() = 0;
+
+  virtual const ViewportMetrics& GetViewportMetrics() = 0;
+};
 
 }  // namespace ws
 }  // namespace mus
 
-#endif  // COMPONENTS_MUS_WS_SERVER_WINDOW_TRACKER_H_
+#endif  // COMPONENTS_MUS_WS_FRAME_GENERATOR_DELEGATE_H_