Change CaptureSynchronizer and PointerWatcherEventRouter to support multiple CaptureClients.

ui/views/widget/desktop_aura/desktop_capture_client.cc

Index: ui/views/widget/desktop_aura/desktop_capture_client.cc
diff --git a/ui/views/widget/desktop_aura/desktop_capture_client.cc b/ui/views/widget/desktop_aura/desktop_capture_client.cc
index 5ce64e9d025154dfaedc259308675d4446709e43..2ead484c78110890be40f91c1fc19a40c0a4e138 100644
--- a/ui/views/widget/desktop_aura/desktop_capture_client.cc
+++ b/ui/views/widget/desktop_aura/desktop_capture_client.cc
@@ -4,6 +4,7 @@
 
 #include "ui/views/widget/desktop_aura/desktop_capture_client.h"
 
+#include "ui/aura/client/capture_client_observer.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_tracker.h"
@@ -77,6 +78,9 @@ void DesktopCaptureClient::SetCapture(aura::Window* new_capture_window) {
       }
     }
   }  // else case is capture is remaining in our root, nothing to do.
+
+  for (aura::client::CaptureClientObserver& observer : observers_)
+    observer.OnCaptureChanged(old_capture_window, capture_window_);
 }
 
 void DesktopCaptureClient::ReleaseCapture(aura::Window* window) {
@@ -100,12 +104,12 @@ aura::Window* DesktopCaptureClient::GetGlobalCaptureWindow() {
 
 void DesktopCaptureClient::AddObserver(
     aura::client::CaptureClientObserver* observer) {
-  NOTREACHED();
+  observers_.AddObserver(observer);
 }
 
 void DesktopCaptureClient::RemoveObserver(
     aura::client::CaptureClientObserver* observer) {
-  NOTREACHED();
+  observers_.RemoveObserver(observer);
 }
 
 }  // namespace views