Don't allow events to be swallowed by MdFocusRing.

ui/views/controls/button/custom_button.cc

Index: ui/views/controls/button/custom_button.cc
diff --git a/ui/views/controls/button/custom_button.cc b/ui/views/controls/button/custom_button.cc
index 9a0e28a65a5e92a62935741c130cbb0fb2dd4962..c99fcaacb72310a5b0ee26654b7f84a0d5370a9a 100644
--- a/ui/views/controls/button/custom_button.cc
+++ b/ui/views/controls/button/custom_button.cc
@@ -48,6 +48,9 @@ class MdFocusRing : public views::View {
   MdFocusRing() {
     SetPaintToLayer(true);
     layer()->SetFillsBoundsOpaquely(false);
+
+    // Don't accept input events.
+    SetEnabled(false);
   }
   ~MdFocusRing() override {}