Change CaptureSynchronizer and PointerWatcherEventRouter to support multiple CaptureClients.

ui/views/mus/pointer_watcher_event_router.cc

Index: ui/views/mus/pointer_watcher_event_router.cc
diff --git a/ui/views/mus/pointer_watcher_event_router.cc b/ui/views/mus/pointer_watcher_event_router.cc
index 26b4c06683ee813d1c77ba5a7c0c9ffe4c064b3a..3daf94c0c3ac9f78b1fb5efd3c4f803bf31d8b7c 100644
--- a/ui/views/mus/pointer_watcher_event_router.cc
+++ b/ui/views/mus/pointer_watcher_event_router.cc
@@ -27,14 +27,11 @@ PointerWatcherEventRouter::PointerWatcherEventRouter(
     aura::WindowTreeClient* window_tree_client)
     : window_tree_client_(window_tree_client) {
   window_tree_client->AddObserver(this);
-  window_tree_client_->GetCaptureClient()->AddObserver(this);
 }
 
 PointerWatcherEventRouter::~PointerWatcherEventRouter() {
-  if (window_tree_client_) {
+  if (window_tree_client_)
     window_tree_client_->RemoveObserver(this);
-    window_tree_client_->GetCaptureClient()->RemoveObserver(this);
-  }
 }
 
 void PointerWatcherEventRouter::AddPointerWatcher(PointerWatcher* watcher,
@@ -132,6 +129,16 @@ void PointerWatcherEventRouter::OnPointerEventObserved(
   }
 }
 
+void PointerWatcherEventRouter::AttachToCaptureClient(
+    aura::client::CaptureClient* capture_client) {
+  capture_client->AddObserver(this);
+}
+
+void PointerWatcherEventRouter::DetachFromCaptureClient(
+    aura::client::CaptureClient* capture_client) {
+  capture_client->RemoveObserver(this);
+}
+
 PointerWatcherEventRouter::EventTypes
 PointerWatcherEventRouter::DetermineEventTypes() {
   if (HasPointerWatcher(&move_watchers_))
@@ -161,7 +168,6 @@ void PointerWatcherEventRouter::OnDidDestroyClient(
   // We expect that all observers have been removed by this time.
   DCHECK_EQ(event_types_, EventTypes::NONE);
   DCHECK_EQ(client, window_tree_client_);
-  window_tree_client_->GetCaptureClient()->RemoveObserver(this);
   window_tree_client_->RemoveObserver(this);
   window_tree_client_ = nullptr;

[sadrul, 2017/01/30 19:37:58]

It would make sense to continue to RemoveObserver from |client|.

[riajiang, 2017/01/30 20:24:09]

I thought that by the time the WindowTreeClient is being destroyed, the
PointerWatcherEventRouter should have already removed itself as an observer for
all the CaptureClients (when DesktopWindowTreeHostMus gets closed and when
WindowManager gets shut down)? And now that we don't just have one capture
client anymore, we can't get the one capture client from WindowTreeClient?

[sadrul, 2017/01/30 20:52:12]

Oh yeah, of course. You are right.

 }