mus: Let clients set the cursor of their window.

components/mus/public/cpp/lib/window.cc

Index: components/mus/public/cpp/lib/window.cc
diff --git a/components/mus/public/cpp/lib/window.cc b/components/mus/public/cpp/lib/window.cc
index 8dffc7f52d010f64002e31389124d3b7af0c2530..9fa469b6dd135d0ba53e02980e9b9b9bc4ca9c25 100644
--- a/components/mus/public/cpp/lib/window.cc
+++ b/components/mus/public/cpp/lib/window.cc
@@ -362,6 +362,11 @@ void Window::SetCanFocus(bool can_focus) {
     tree_client()->SetCanFocus(id_, can_focus);
 }
 
+void Window::SetStandardCursor(mus::mojom::Cursor cursor_id) {
+  if (connection_)
+    tree_client()->SetStandardCursor(id_, cursor_id);

[sky, 2015/12/01 21:48:00]

In general we tend to assume the change is going to take, which means this
should notify observers immediately.

+}
+
 void Window::Embed(mus::mojom::WindowTreeClientPtr client) {
   Embed(client.Pass(), mus::mojom::WindowTree::ACCESS_POLICY_DEFAULT,
         base::Bind(&EmptyEmbedCallback));