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..76a9b504c0883d6c64f12244fe4ea81c04013425 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();
 }
 
+AshCursorPlatformDelegate* ShellTestApi::ash_cursor_platform_delegate() {
+  return shell_->cursor_platform_delegate_;
+}
+
 LauncherModel* ShellTestApi::launcher_model() {
   return shell_->launcher_model_.get();
 }