mus: Implement ScreenMus::GetCursorScreenPoint().

components/mus/ws/user_display_manager.h

Index: components/mus/ws/user_display_manager.h
diff --git a/components/mus/ws/user_display_manager.h b/components/mus/ws/user_display_manager.h
index c17a7c6981a155821d53159ac3482e8ddaedc8ad..65c1787ffb8b599a03712568867abf2237d8c3a9 100644
--- a/components/mus/ws/user_display_manager.h
+++ b/components/mus/ws/user_display_manager.h
@@ -7,12 +7,17 @@
 
 #include <set>
 
+#include "base/atomicops.h"
 #include "base/macros.h"
 #include "components/mus/public/interfaces/display.mojom.h"
 #include "components/mus/ws/user_id.h"
 #include "mojo/public/cpp/bindings/binding_set.h"
 #include "mojo/public/cpp/bindings/interface_ptr_set.h"
 
+namespace gfx {
+class Point;
+}
+
 namespace mus {
 namespace ws {
 
@@ -39,6 +44,14 @@ class UserDisplayManager : public mojom::DisplayManager {
   // Called by Display prior to |display| being removed and destroyed.
   void OnWillDestroyDisplay(Display* display);
 
+  // Called from WindowManagerState when its EventDispatcher receives a mouse
+  // event.
+  void OnMouseCursorLocationChanged(const gfx::Point& point);
+
+  // Returns a read-only handle to the shared memory which contains the global
+  // mouse cursor position. Each call returns a new handle.
+  mojo::ScopedSharedBufferHandle GetCursorLocationMemory();
+
  private:
   friend class test::UserDisplayManagerTestApi;
 
@@ -74,6 +87,20 @@ class UserDisplayManager : public mojom::DisplayManager {
   // Observer used for tests.
   mojom::DisplayManagerObserver* test_observer_ = nullptr;
 
+  // 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::Atomic32 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 int32 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::Atomic32* cursor_location_memory_;
+
   DISALLOW_COPY_AND_ASSIGN(UserDisplayManager);
 };