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 c119342098cc1fec00a0a41ce77efd758358193f..68a86b302074ee3899597af8732d48753a0061e5 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 {}