Mozart: Implement basic input event dispatch with hit testing.

apps/moterm/moterm_view.cc

Index: apps/moterm/moterm_view.cc
diff --git a/apps/moterm/moterm_view.cc b/apps/moterm/moterm_view.cc
index 2c286e4f553403195c3ae94c559cd7c82bcfdff0..162e997a5c0b73e8ab224b87a3e18f6b0cf9db51 100644
--- a/apps/moterm/moterm_view.cc
+++ b/apps/moterm/moterm_view.cc
@@ -239,6 +239,7 @@ void MotermView::OnDraw(const mojo::gfx::composition::FrameInfo& frame_info,
   update->resources.insert(kMotermImageResourceId, moterm_resource.Pass());
 
   auto root_node = mojo::gfx::composition::Node::New();
+  root_node->hit_test_behavior = mojo::gfx::composition::HitTestBehavior::New();
   root_node->op = mojo::gfx::composition::NodeOp::New();
   root_node->op->set_image(mojo::gfx::composition::ImageNodeOp::New());
   root_node->op->get_image()->content_rect = bounds.Clone();