Rework ash::CursorManager into a corewm object, to share code with desktop.

ash/test/shell_test_api.cc

Index: ash/test/shell_test_api.cc
diff --git a/ash/test/shell_test_api.cc b/ash/test/shell_test_api.cc
index 03dbb3af1c50ea7d8cf9fe8c6eb1295c21446469..f4ba794665dc4cc188b3be1c90f88eeee06aac52 100644
--- a/ash/test/shell_test_api.cc
+++ b/ash/test/shell_test_api.cc
@@ -35,6 +35,10 @@ ShellTestApi::screen_position_controller() {
   return shell_->screen_position_controller_.get();
 }
 
+AshNativeCursorManager* ShellTestApi::ash_native_cursor_manager() {
+  return shell_->native_cursor_manager_;
+}
+
 LauncherModel* ShellTestApi::launcher_model() {
   return shell_->launcher_model_.get();
 }