Fixes a crash when InkDropDelegate gets destroyed after its InkDropHost

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 bfc356c595d5577d1ee7e8e73347e5a8a0f68ed1..c41967a57931d5081e6946048013c5c3c8c39756 100644
--- a/ui/views/controls/button/custom_button.cc
+++ b/ui/views/controls/button/custom_button.cc
@@ -56,6 +56,9 @@ CustomButton* CustomButton::AsCustomButton(views::View* view) {
 }
 
 CustomButton::~CustomButton() {
+  // InkDropDelegate needs to be destroyed by now since it may need to call
+  // methods on |this| via InkDropHost.
+  DCHECK(!ink_drop_delegate_);
 }
 
 void CustomButton::SetState(ButtonState state) {