mus: Implement ScreenMus::GetCursorScreenPoint().

components/mus/public/cpp/window_tree_connection.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_H_
 #define COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "components/mus/common/types.h"
 #include "components/mus/public/interfaces/window_tree.mojom.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 
+namespace gfx {
+class Point;
+}
+
 namespace shell {
 class Connector;
 }
 
 namespace mus {
 
 class Window;
 class WindowManagerDelegate;
 class WindowTreeConnectionObserver;
 class WindowTreeDelegate;
@@ skipping 42 matching lines @@
   // input capture, or if another app has capture.
   virtual Window* GetCaptureWindow() = 0;
 
   // Returns the focused window; null if focus is not yet known or another app
   // is focused.
   virtual Window* GetFocusedWindow() = 0;
 
   // Sets focus to null. This does nothing if focus is currently null.
   virtual void ClearFocus() = 0;
 
+  // Performs additional initialization so that we can synchronously retrieve
+  // the cursor location.
+  virtual void InitializeCursorLocation() = 0;

[sky, 2016/04/27 20:10:28]

It seems like what you have implemented is pretty light weight, and we should
just do it all the time. WDYT?

+
+  // Returns the current location of the mouse on screen. Note: this method may
+  // race the asynchronous initialization; but in that case we return (0, 0).
+  virtual gfx::Point GetCursorScreenPoint() = 0;
+
   // Creates and returns a new Window (which is owned by the window server).
   // Windows are initially hidden, use SetVisible(true) to show.
   Window* NewWindow() { return NewWindow(nullptr); }
   virtual Window* NewWindow(
       const std::map<std::string, std::vector<uint8_t>>* properties) = 0;
   virtual Window* NewTopLevelWindow(
       const std::map<std::string, std::vector<uint8_t>>* properties) = 0;
 
   // Returns the id for this connection.
   // TODO(sky): remove this. It is not necessarily correct anymore.
   virtual ConnectionSpecificId GetConnectionId() = 0;
 
   virtual void AddObserver(WindowTreeConnectionObserver* observer) = 0;
   virtual void RemoveObserver(WindowTreeConnectionObserver* observer) = 0;
 };
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_H_