mus: Fix a teardown crash.

services/ui/ws/frame_generator.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_FRAME_GENERATOR_H_
 #define SERVICES_UI_WS_FRAME_GENERATOR_H_
 
 #include <memory>
 #include <unordered_map>
 
 #include "base/macros.h"
 #include "base/timer/timer.h"
 #include "cc/surfaces/frame_sink_id.h"
 #include "cc/surfaces/local_frame_id.h"
 #include "cc/surfaces/surface_sequence.h"
 #include "cc/surfaces/surface_sequence_generator.h"
-#include "services/ui/ws/server_window_observer.h"
+#include "services/ui/ws/server_window_tracker.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace cc {
 class CompositorFrame;
 class CopyOutputRequest;
 class RenderPass;
 class SurfaceId;
 }
 
@@ skipping 11 matching lines @@
 namespace test {
 class FrameGeneratorTest;
 }
 
 class FrameGeneratorDelegate;
 class ServerWindow;
 class ServerWindowCompositorFrameSink;
 
 // Responsible for redrawing the display in response to the redraw requests by
 // submitting CompositorFrames to the owned CompositorFrameSink.
-class FrameGenerator : public ServerWindowObserver {
+class FrameGenerator : public ServerWindowTracker {
  public:
   FrameGenerator(FrameGeneratorDelegate* delegate,
                  scoped_refptr<DisplayCompositor> display_compositor);
   ~FrameGenerator() override;
 
   void OnGpuChannelEstablished(scoped_refptr<gpu::GpuChannelHost> gpu_channel);
 
   // Schedules a redraw for the provided region.
   void RequestRedraw(const gfx::Rect& redraw_region);
   void OnAcceleratedWidgetAvailable(gfx::AcceleratedWidget widget);
@@ skipping 75 matching lines @@
   base::WeakPtrFactory<FrameGenerator> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(FrameGenerator);
 };
 
 }  // namespace ws
 
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_FRAME_GENERATOR_H_