X11: Add TestDesktopScreenX11 to simulate mouse movement in ui tests

ui/views/widget/desktop_aura/desktop_screen_x11.cc

Index: ui/views/widget/desktop_aura/desktop_screen_x11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_screen_x11.cc b/ui/views/widget/desktop_aura/desktop_screen_x11.cc
index d3d2315bce9cb981ed62c4ab33d61c80d3616150..f0ada13946acc1e2cd324d45ae8c9e807c97fc6a 100644
--- a/ui/views/widget/desktop_aura/desktop_screen_x11.cc
+++ b/ui/views/widget/desktop_aura/desktop_screen_x11.cc
@@ -405,9 +405,31 @@ void DesktopScreenX11::SetDisplaysInternal(
 }
 
 ////////////////////////////////////////////////////////////////////////////////
+// TestDesktopScreenX11, public:
+
+TestDesktopScreenX11::TestDesktopScreenX11() {}
+
+TestDesktopScreenX11::~TestDesktopScreenX11() {}
+
+gfx::Point TestDesktopScreenX11::GetCursorScreenPoint() {
+  return cursor_screen_point_;
+}
+
+void TestDesktopScreenX11::SetCursorScreenPoint(const gfx::Point& point) {
+  cursor_screen_point_ = point;
+}
+
+////////////////////////////////////////////////////////////////////////////////
 
 display::Screen* CreateDesktopScreen() {
   return new DesktopScreenX11;
 }
 
+TestDesktopScreenX11* GetTestDesktopScreenX11() {
+  static std::unique_ptr<TestDesktopScreenX11> test_screen_instance;
+  if (!test_screen_instance.get())
+    test_screen_instance.reset(new TestDesktopScreenX11());
+  return test_screen_instance.get();
+}
+
 }  // namespace views