So far there are multiple APIs regarding hit-testing in aura -- things within aura::WindowTargeter (WindowTargeter::SetInsets, GetHitTestsRect, etc) and things within aura::Window and aura::WindowDelegate (Window::HitTest, Window::GetEventHandlerForPoint, WindowDelegate::HasHitTestMask, WindowDelegate::GetHitTestMask).

This situation is confusing. For Mash, we are inclined into the WindowTargeter methods and Window/WindowDelegate methods will not be supported -- and WindowDelegate::GetHitTestMask is too generic (it can draw any shapes as gfx::Path while WindowTargeter supports only a vector of gfx::Rects). We may want to migrate Window's usages of hit-test to WindowTargeter, and then remove those methods.