mus: Implement ScreenMus::GetCursorScreenPoint().

components/mus/ws/window_manager_state.h

Index: components/mus/ws/window_manager_state.h
diff --git a/components/mus/ws/window_manager_state.h b/components/mus/ws/window_manager_state.h
index d85199b5f4be81f06963dc6299e29f18a8050499..e742c9dc057c299ba8dc7ed66e74e5af44aed0ec 100644
--- a/components/mus/ws/window_manager_state.h
+++ b/components/mus/ws/window_manager_state.h
@@ -7,6 +7,7 @@
 
 #include <stdint.h>
 
+#include "base/atomicops.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/timer/timer.h"
@@ -106,6 +107,8 @@ class WindowManagerState : public EventDispatcherDelegate {
 
   void OnWillDestroyTree(WindowTree* tree);
 
+  mojo::ScopedSharedBufferHandle GetCursorLocationMemory();
+
  private:
   class ProcessedEventTarget;
   friend class Display;
@@ -159,6 +162,7 @@ class WindowManagerState : public EventDispatcherDelegate {
   void SetNativeCapture() override;
   void ReleaseNativeCapture() override;
   void OnServerWindowCaptureLost(ServerWindow* window) override;
+  void OnMouseCursorLocationChanged(const gfx::Point& point) override;
   void DispatchInputEventToWindow(ServerWindow* target,
                                   bool in_nonclient_area,
                                   const ui::Event& event,
@@ -188,6 +192,20 @@ class WindowManagerState : public EventDispatcherDelegate {
 
   EventDispatcher event_dispatcher_;
 
+  // The current location of the cursor. This is always kept up to date so we
+  // can atomically write this to |cursor_location_memory_| once it is created.
+  base::subtle::Atomic64 current_cursor_location_;
+
+  // A handle to a shared memory buffer that is one 64 bit integer long. We
+  // share this with any connection as the same user. This buffer is lazily
+  // created on the first access.
+  mojo::ScopedSharedBufferHandle cursor_location_handle_;
+
+  // The one int64 in |cursor_location_handle_|. When we write to this
+  // location, we must always write to it atomically. (On the other side of the
+  // mojo connection, this data must be read atomically.)
+  base::subtle::Atomic64* cursor_location_memory_;
+
   DISALLOW_COPY_AND_ASSIGN(WindowManagerState);
 };