Change CaptureSynchronizer and PointerWatcherEventRouter to support multiple CaptureClients.

ui/aura/mus/capture_synchronizer.h

Index: ui/aura/mus/capture_synchronizer.h
diff --git a/ui/aura/mus/capture_synchronizer.h b/ui/aura/mus/capture_synchronizer.h
index 87bce872168d8c50d69ab3361b1d2643d8affb9b..71adcbb0dfae10265fd3b6a3fce41706856068d4 100644
--- a/ui/aura/mus/capture_synchronizer.h
+++ b/ui/aura/mus/capture_synchronizer.h
@@ -32,8 +32,7 @@ class CaptureSynchronizer : public WindowObserver,
                             public client::CaptureClientObserver {
  public:
   CaptureSynchronizer(CaptureSynchronizerDelegate* delegate,
-                      ui::mojom::WindowTree* window_tree,
-                      client::CaptureClient* capture_client);
+                      ui::mojom::WindowTree* window_tree);
   ~CaptureSynchronizer() override;
 
   WindowMus* capture_window() { return capture_window_; }
@@ -42,11 +41,16 @@ class CaptureSynchronizer : public WindowObserver,
   void SetCaptureFromServer(WindowMus* window);
 
  private:
+  void Attach(client::CaptureClient* capture_client);
+
   // Internal implementation for capture changes. Adds/removes observer as
   // necessary and sets |capture_window_| to |window|.
   void SetCaptureWindow(WindowMus* window);
 
   // WindowObserver:
+  void OnWindowPropertyChanged(Window* window,
+                               const void* key,
+                               intptr_t old) override;
   void OnWindowDestroying(Window* window) override;
 
   // client::CaptureClientObserver:
@@ -54,7 +58,6 @@ class CaptureSynchronizer : public WindowObserver,
 
   CaptureSynchronizerDelegate* delegate_;
   ui::mojom::WindowTree* window_tree_;
-  client::CaptureClient* capture_client_;
 
   // Window that currently has capture.
   WindowMus* capture_window_ = nullptr;