Change CaptureSynchronizer and PointerWatcherEventRouter to support multiple CaptureClients.

ui/views/mus/mus_client.cc

Index: ui/views/mus/mus_client.cc
diff --git a/ui/views/mus/mus_client.cc b/ui/views/mus/mus_client.cc
index 743ea2847545c2f181efda5157e4b3a916845190..a30260dd0fd766fb89418d966ff22f24fa0e14ef 100644
--- a/ui/views/mus/mus_client.cc
+++ b/ui/views/mus/mus_client.cc
@@ -16,6 +16,7 @@
 #include "services/ui/public/interfaces/event_matcher.mojom.h"
 #include "services/ui/public/interfaces/window_manager.mojom.h"
 #include "ui/aura/env.h"
+#include "ui/aura/mus/capture_synchronizer.h"
 #include "ui/aura/mus/mus_context_factory.h"
 #include "ui/aura/mus/os_exchange_data_provider_mus.h"
 #include "ui/aura/mus/property_converter.h"
@@ -222,6 +223,20 @@ NativeWidget* MusClient::CreateNativeWidget(
   return native_widget;
 }
 
+void MusClient::OnCaptureClientSet(
+    aura::client::CaptureClient* capture_client) {
+  pointer_watcher_event_router_->AttachToCaptureClient(capture_client);
+  window_tree_client_->capture_synchronizer()->AttachToCaptureClient(
+      capture_client);
+}
+
+void MusClient::OnCaptureClientUnset(
+    aura::client::CaptureClient* capture_client) {
+  pointer_watcher_event_router_->DetachFromCaptureClient(capture_client);
+  window_tree_client_->capture_synchronizer()->DetachFromCaptureClient(
+      capture_client);
+}
+
 void MusClient::AddObserver(MusClientObserver* observer) {
   observer_list_.AddObserver(observer);
 }