mus: Implement ScreenMus::GetCursorScreenPoint().

components/mus/ws/window_tree.cc

Index: components/mus/ws/window_tree.cc
diff --git a/components/mus/ws/window_tree.cc b/components/mus/ws/window_tree.cc
index 0114bf5e89484c2ea0a5aa308e023c9861395187..a07f454da7e8da92ce0912f2d28ed6fb2a6cf2c6 100644
--- a/components/mus/ws/window_tree.cc
+++ b/components/mus/ws/window_tree.cc
@@ -673,6 +673,15 @@ WindowManagerState* WindowTree::GetWindowManagerStateForWindowManager() {
   return wms;
 }
 
+WindowManagerState* WindowTree::GetWindowManagerStateForUser() {
+  Display* display = display_manager()->displays().empty()
+                         ? nullptr
+                         : *(display_manager()->displays().begin());
+  return display && user_id_ != InvalidUserId()
+      ? display->GetWindowManagerStateForUser(user_id_)
+      : nullptr;
+}
+
 bool WindowTree::ShouldRouteToWindowManager(const ServerWindow* window) const {
   // If the client created this window, then do not route it through the WM.
   if (window->id().connection_id == id_)
@@ -986,15 +995,8 @@ void WindowTree::NewTopLevelWindow(
     mojo::Map<mojo::String, mojo::Array<uint8_t>> transport_properties) {
   DCHECK(!waiting_for_top_level_window_info_);
   const ClientWindowId client_window_id(transport_window_id);
-  // TODO(sky): need a way for client to provide context to figure out display.
-  Display* display = display_manager()->displays().empty()
-                         ? nullptr
-                         : *(display_manager()->displays().begin());
   // TODO(sky): move checks to accesspolicy.
-  WindowManagerState* wms =
-      display && user_id_ != InvalidUserId()
-          ? display->GetWindowManagerStateForUser(user_id_)
-          : nullptr;
+  WindowManagerState* wms = GetWindowManagerStateForUser();
   if (!wms || wms->tree() == this || !IsValidIdForNewWindow(client_window_id)) {
     client()->OnChangeCompleted(change_id, false);
     return;
@@ -1331,6 +1333,12 @@ void WindowTree::GetWindowManagerClient(
           this, std::move(internal)));
 }
 
+void WindowTree::GetCursorLocationMemory(
+    const GetCursorLocationMemoryCallback& callback) {
+  WindowManagerState* wms = GetWindowManagerStateForUser();
+  callback.Run(wms->GetCursorLocationMemory());
+}
+
 void WindowTree::AddAccelerator(uint32_t id,
                                 mojom::EventMatcherPtr event_matcher,
                                 const AddAcceleratorCallback& callback) {