Factor draw functionality out of DefaultPlatformDisplay into FrameGenerator.

services/ui/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 SERVICES_UI_WS_USER_ID_TRACKER_OBSERVER_H_
-#define SERVICES_UI_WS_USER_ID_TRACKER_OBSERVER_H_
+#ifndef SERVICES_UI_WS_FRAME_GENERATOR_DELEGATE_H_
+#define SERVICES_UI_WS_FRAME_GENERATOR_DELEGATE_H_
 
-#include <stdint.h>
-
-#include "services/ui/ws/user_id.h"
+#include "base/macros.h"
 
 namespace ui {
 namespace ws {
 
-class UserIdTrackerObserver {
+class ServerWindow;
+
+struct ViewportMetrics {
+  gfx::Size size_in_pixels;
+  float device_scale_factor = 0.f;
+};
+
+class FrameGeneratorDelegate {
  public:
-  virtual void OnActiveUserIdChanged(const UserId& previously_active_id,
-                                     const UserId& active_id) {}
-  virtual void OnUserIdAdded(const UserId& id) {}
-  virtual void OnUserIdRemoved(const UserId& id) {}
+  // 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;
 
  protected:
-  virtual ~UserIdTrackerObserver() {}
+  virtual ~FrameGeneratorDelegate() {}
 };
 
 }  // namespace ws
 }  // namespace ui
 
-#endif  // SERVICES_UI_WS_USER_ID_TRACKER_OBSERVER_H_
+#endif  // SERVICES_UI_WS_FRAME_GENERATOR_DELEGATE_H_