Change CaptureSynchronizer and PointerWatcherEventRouter to support multiple CaptureClients.

ui/views/widget/desktop_aura/desktop_capture_client.h

Index: ui/views/widget/desktop_aura/desktop_capture_client.h
diff --git a/ui/views/widget/desktop_aura/desktop_capture_client.h b/ui/views/widget/desktop_aura/desktop_capture_client.h
index 497e896ff5ba3638247619e11a3e4704c0e00173..1f19ec64fa5f592b7277949370d41849fa6b5d97 100644
--- a/ui/views/widget/desktop_aura/desktop_capture_client.h
+++ b/ui/views/widget/desktop_aura/desktop_capture_client.h
@@ -9,6 +9,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/views/views_export.h"
 
@@ -57,6 +58,8 @@ class VIEWS_EXPORT DesktopCaptureClient : public aura::client::CaptureClient {
   // Set of DesktopCaptureClients.
   static CaptureClients* capture_clients_;
 
+  base::ObserverList<aura::client::CaptureClientObserver> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(DesktopCaptureClient);
 };