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

services/ui/demo/mus_demo.cc

Index: services/ui/demo/mus_demo.cc
diff --git a/services/ui/demo/mus_demo.cc b/services/ui/demo/mus_demo.cc
index 0fbcd356c25475ef3794f4687541853891d9582f..0ae145c089fcc1878d5d867fd31b48437151a9c0 100644
--- a/services/ui/demo/mus_demo.cc
+++ b/services/ui/demo/mus_demo.cc
@@ -118,6 +118,10 @@
 void MusDemo::OnPointerEventObserved(const PointerEvent& event,
                                      aura::Window* target) {}
 
+aura::client::CaptureClient* MusDemo::GetCaptureClient() {
+  return capture_client_.get();
+}
+
 aura::PropertyConverter* MusDemo::GetPropertyConverter() {
   return property_converter_.get();
 }