CustomButton: restrict animation repaints to buttons that actually animate

ui/views/examples/button_example.h

Index: ui/views/examples/button_example.h
diff --git a/ui/views/examples/button_example.h b/ui/views/examples/button_example.h
index 956759cf412c0d808eb21bd843f2e4603087cf8c..81ace6738b8192f2f979e0e25df1b2ba8841c72c 100644
--- a/ui/views/examples/button_example.h
+++ b/ui/views/examples/button_example.h
@@ -13,6 +13,7 @@ namespace views {
 
 class ImageButton;
 class LabelButton;
+class MdTextButton;
 
 namespace examples {
 
@@ -36,6 +37,9 @@ class VIEWS_EXAMPLES_EXPORT ButtonExample : public ExampleBase,
   LabelButton* label_button_ = nullptr;
   LabelButton* styled_button_ = nullptr;
   LabelButton* disabled_button_ = nullptr;
+  MdTextButton* md_button_ = nullptr;
+  MdTextButton* md_default_button_ = nullptr;
+  MdTextButton* md_prominent_button_ = nullptr;
   ImageButton* image_button_ = nullptr;
 
   const gfx::ImageSkia* icon_ = nullptr;