mus: Implement ScreenMus::GetCursorScreenPoint().

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

Index: components/mus/public/cpp/lib/window_tree_client_impl.cc
diff --git a/components/mus/public/cpp/lib/window_tree_client_impl.cc b/components/mus/public/cpp/lib/window_tree_client_impl.cc
index 9b199da20cc8d1fb99f9ed7d151ce3152a046265..989b23fd7d4611e2378383be02e22a21c69198cf 100644
--- a/components/mus/public/cpp/lib/window_tree_client_impl.cc
+++ b/components/mus/public/cpp/lib/window_tree_client_impl.cc
@@ -9,6 +9,7 @@
 
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
+#include "base/threading/thread_restrictions.h"
 #include "components/mus/common/util.h"
 #include "components/mus/public/cpp/input_event_handler.h"
 #include "components/mus/public/cpp/lib/in_flight_change.h"
@@ -814,6 +815,13 @@ Window* WindowTreeClientImpl::GetCaptureWindow() {
   return capture_window_;
 }
 
+gfx::Point WindowTreeClientImpl::GetCursorScreenPoint() {
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;

[sky, 2016/04/18 15:09:11]

Add a TODO that this code should use the location from the current event if
we're in the process of dispatching one. We can't do that until James lands
https://codereview.chromium.org/1883263002/ .

+  mojo::PointPtr p;
+  tree_ptr_->GetCursorScreenPoint(&p);
+  return p.To<gfx::Point>();
+}
+
 void WindowTreeClientImpl::OnWindowVisibilityChanged(Id window_id,
                                                      bool visible) {
   Window* window = GetWindowByServerId(window_id);