Revert: Remove WindowTreeClientDelegate::GetCaptureClient() and WindowTreeClient::GetCaptureClient()

ash/mus/window_manager.cc

Index: ash/mus/window_manager.cc
diff --git a/ash/mus/window_manager.cc b/ash/mus/window_manager.cc
index 1ca6846e70a179079e48947c03af03e80d4b152d..c0233919f382d46d17f9630b54832f46aaf14b50 100644
--- a/ash/mus/window_manager.cc
+++ b/ash/mus/window_manager.cc
@@ -293,6 +293,10 @@
   pointer_watcher_event_router_->OnPointerEventObserved(event, target);
 }
 
+aura::client::CaptureClient* WindowManager::GetCaptureClient() {
+  return wm_state_->capture_controller();
+}
+
 aura::PropertyConverter* WindowManager::GetPropertyConverter() {
   return property_converter_.get();
 }