Change CaptureSynchronizer and PointerWatcherEventRouter to support multiple CaptureClients.

ui/views/mus/mus_client.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/mus/mus_client.h"
 
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
 #include "base/threading/thread.h"
 #include "components/discardable_memory/client/client_discardable_shared_memory_manager.h"
@@ skipping 203 matching lines @@
   } else {
     std::map<std::string, std::vector<uint8_t>> mus_properties =
         ConfigurePropertiesFromParams(init_params);
     native_widget->SetDesktopWindowTreeHost(
         base::MakeUnique<DesktopWindowTreeHostMus>(delegate, native_widget,
                                                    &mus_properties));
   }
   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);
 }
 
 void MusClient::RemoveObserver(MusClientObserver* observer) {
   observer_list_.RemoveObserver(observer);
 }
 
 void MusClient::OnEmbed(
     std::unique_ptr<aura::WindowTreeHostMus> window_tree_host) {
@@ skipping 38 matching lines @@
       return root->GetTopWindowContainingPoint(relative_point);
   }
   return nullptr;
 }
 
 std::unique_ptr<OSExchangeData::Provider> MusClient::BuildProvider() {
   return base::MakeUnique<aura::OSExchangeDataProviderMus>();
 }
 
 }  // namespace views