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 2e23362a94c80b3ec662622ef9ecd2b1fa94a4c4..2474945c7d885af623e33ae5873f603f6cbd2172 100644
--- a/ui/views/mus/mus_client.cc
+++ b/ui/views/mus/mus_client.cc
@@ -221,6 +221,18 @@ NativeWidget* MusClient::CreateNativeWidget(
   return native_widget;
 }
 
+void MusClient::OnCaptureClientSet(
+    aura::client::CaptureClient* capture_client) {
+  capture_client->AddObserver(pointer_watcher_event_router_.get());
+  window_tree_client_->OnCaptureClientSet(capture_client);

[sadrul, 2017/01/27 01:06:54]

Maybe do:

  pointer_watcher_event_router_->AttachToClient(capture_client);
  window_tree_client_->capture_synchronizer()->AttachToClient(capture_client);

I feel like that would make this simpler.

[riajiang, 2017/01/30 18:36:22]

Sure that makes sense. Changed to expose capture_synchronizer from
WindowTreeClient and call that directly. But had to make CaptureSynchronizer
AURA_EXPORT.

+}
+
+void MusClient::OnCaptureClientUnset(
+    aura::client::CaptureClient* capture_client) {
+  capture_client->RemoveObserver(pointer_watcher_event_router_.get());
+  window_tree_client_->OnCaptureClientUnset(capture_client);
+}
+
 void MusClient::AddObserver(MusClientObserver* observer) {
   observer_list_.AddObserver(observer);
 }