Change CaptureSynchronizer and PointerWatcherEventRouter to support multiple CaptureClients.

ui/aura/mus/capture_synchronizer.cc

Index: ui/aura/mus/capture_synchronizer.cc
diff --git a/ui/aura/mus/capture_synchronizer.cc b/ui/aura/mus/capture_synchronizer.cc
index 67dacb4e9d5672b55204f2980242e71c5ca52f0f..62190e94cca65c83dae74847dc931d3cf39d48e0 100644
--- a/ui/aura/mus/capture_synchronizer.cc
+++ b/ui/aura/mus/capture_synchronizer.cc
@@ -14,30 +14,37 @@
 namespace aura {
 
 CaptureSynchronizer::CaptureSynchronizer(CaptureSynchronizerDelegate* delegate,
-                                         ui::mojom::WindowTree* window_tree,
-                                         client::CaptureClient* capture_client)
-    : delegate_(delegate),
-      window_tree_(window_tree),
-      capture_client_(capture_client) {
-  capture_client_->AddObserver(this);
-}
+                                         ui::mojom::WindowTree* window_tree)
+    : delegate_(delegate), window_tree_(window_tree) {}
 
-CaptureSynchronizer::~CaptureSynchronizer() {
-  SetCaptureWindow(nullptr);
-  capture_client_->RemoveObserver(this);
-}
+CaptureSynchronizer::~CaptureSynchronizer() {}
 
 void CaptureSynchronizer::SetCaptureFromServer(WindowMus* window) {
   if (window == capture_window_)
     return;
 
   DCHECK(!setting_capture_);
-  // Don't immediately set |capture_client_|. It's possible the change will be
+  // Don't immediately set capture client. It's possible the change will be

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

We do not set the capture client anymore (since we don't track a single capture
client). Maybe something like:

"""Don't immediately set |capture_window_|. It's possible the change
will be rejected. |capture_window_| is set in OnCaptureChanged() if
capture succeeds."""

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

Done.

   // rejected.
   base::AutoReset<bool> capture_reset(&setting_capture_, true);
   base::AutoReset<WindowMus*> window_setting_capture_to_reset(
       &window_setting_capture_to_, window);
-  capture_client_->SetCapture(window ? window->GetWindow() : nullptr);
+  client::CaptureClient* capture_client =
+      window ? client::GetCaptureClient(window->GetWindow()->GetRootWindow())
+             : client::GetCaptureClient(
+                   capture_window_->GetWindow()->GetRootWindow());
+  capture_client->SetCapture(window ? window->GetWindow() : nullptr);
+}
+
+void CaptureSynchronizer::AttachToCaptureClient(
+    client::CaptureClient* capture_client) {
+  capture_client->AddObserver(this);
+}
+
+void CaptureSynchronizer::DetachFromCaptureClient(
+    client::CaptureClient* capture_client) {
+  SetCaptureWindow(nullptr);
+  capture_client->RemoveObserver(this);
 }
 
 void CaptureSynchronizer::SetCaptureWindow(WindowMus* window) {
@@ -62,6 +69,12 @@ void CaptureSynchronizer::OnCaptureChanged(Window* lost_capture,
   if (!gained_capture && !capture_window_)
     return;  // Happens if the window is deleted during notification.
 
+  // Happens if the window that just lost capture is not the most updated window
+  // that has capture to avoid setting the current capture_window_ to null by
+  // accident.

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

This probably needs some farther explanation, e.g. mention how this can happen
when multiple capture-clients are involved.

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

Updated the comment. WDYT?

+  if (!gained_capture && lost_capture != capture_window_->GetWindow())
+    return;
+
   WindowMus* gained_capture_mus = WindowMus::Get(gained_capture);
   if (setting_capture_ && gained_capture_mus == window_setting_capture_to_) {
     SetCaptureWindow(gained_capture_mus);