Mozart: Implement basic input event dispatch with hit testing.

examples/ui/pdf_viewer/pdf_viewer.cc

Index: examples/ui/pdf_viewer/pdf_viewer.cc
diff --git a/examples/ui/pdf_viewer/pdf_viewer.cc b/examples/ui/pdf_viewer/pdf_viewer.cc
index 3833dba049e4bdee998994c9c2301235fd41bf02..0efcc20ea873339a6de0ab3751f66987ab2e67e8 100644
--- a/examples/ui/pdf_viewer/pdf_viewer.cc
+++ b/examples/ui/pdf_viewer/pdf_viewer.cc
@@ -186,6 +186,8 @@ class PDFDocumentView : public mojo::ui::GaneshView,
     update->resources.insert(kContentImageResourceId, content_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();