Adjust shadow and stroke of MdTextButton.

ui/views/controls/button/md_text_button.h

Index: ui/views/controls/button/md_text_button.h
diff --git a/ui/views/controls/button/md_text_button.h b/ui/views/controls/button/md_text_button.h
index 6d38dc001fef47acaa8eea09297a7f27c82cf8a1..0ec17642c2cf74e3b17060c219a4fa45e18fcf1a 100644
--- a/ui/views/controls/button/md_text_button.h
+++ b/ui/views/controls/button/md_text_button.h
@@ -26,7 +26,9 @@ class VIEWS_EXPORT MdTextButton : public LabelButton {
 
   // See |is_prominent_|.
   void SetProminent(bool is_prominent);
-  void set_bg_color_override(SkColor color) { bg_color_override_ = color; }
+
+  // See |bg_color_override_|.
+  void SetBgColorOverride(const base::Optional<SkColor>& color);
 
   // LabelButton:
   void OnFocus() override;