mus: Implement ScreenMus::GetCursorScreenPoint().

components/mus/public/cpp/window_tree_connection.h

Index: components/mus/public/cpp/window_tree_connection.h
diff --git a/components/mus/public/cpp/window_tree_connection.h b/components/mus/public/cpp/window_tree_connection.h
index daa2f682a8dd683c688fc25033fd7f2ab80e52b9..55df4a3aa8102fbf7f886c508c9a6f38647f1dbc 100644
--- a/components/mus/public/cpp/window_tree_connection.h
+++ b/components/mus/public/cpp/window_tree_connection.h
@@ -15,6 +15,10 @@
 #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;
 }
@@ -77,6 +81,14 @@ class WindowTreeConnection {
   // 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); }