Fix WindowTreeClient::RequestClose(window_id).

ui/aura/mus/window_tree_client.cc

Index: ui/aura/mus/window_tree_client.cc
diff --git a/ui/aura/mus/window_tree_client.cc b/ui/aura/mus/window_tree_client.cc
index e9d1c0772d7a3ed3e42a9dae278a8516cec18268..3113b6a286244b0037d7f48b2cf2b222495b43c2 100644
--- a/ui/aura/mus/window_tree_client.cc
+++ b/ui/aura/mus/window_tree_client.cc
@@ -1314,7 +1314,9 @@ void WindowTreeClient::RequestClose(uint32_t window_id) {
   if (!window || !IsRoot(window))
     return;
 
-  window->GetWindow()->delegate()->OnRequestClose();

[sadrul, 2017/01/05 02:49:00]

I think WindowDelegate::OnRequestClose() can now be removed, since this was the
only place that called it?

+  // Since the window is the root window, we send close request to the entire
+  // WindowTreeHost.
+  GetWindowTreeHostMus(window->GetWindow())->OnCloseRequest();
 }
 
 void WindowTreeClient::OnConnect(ClientSpecificId client_id) {