Introduce new flag to control usage of MD in secondary (not top-chrome)

ui/views/controls/button/label_button.h

Index: ui/views/controls/button/label_button.h
diff --git a/ui/views/controls/button/label_button.h b/ui/views/controls/button/label_button.h
index 1fbb00315a4a254de6426a5ba626fe67937dbf87..bc91661325a2f639bc9509ef479588a58831a75b 100644
--- a/ui/views/controls/button/label_button.h
+++ b/ui/views/controls/button/label_button.h
@@ -131,6 +131,10 @@ class VIEWS_EXPORT LabelButton : public CustomButton,
   // Resets colors from the NativeTheme, explicitly set colors are unchanged.
   virtual void ResetColorsFromNativeTheme();
 
+  // Changes the visual styling of this button to reflect the state of
+  // |is_default()|.
+  virtual void UpdateStyleForDefaultness();

[sky, 2016/05/05 15:40:12]

defaultness? How about just UpdateStyleForDefault?

[Evan Stade, 2016/05/05 15:54:07]

if I don't put the -ness it seems easier to misinterpret, e.g. "update the style
if this button is default". I think the problem is that "default" is the wrong
part of speech (an adjective) whereas defaultness, or defaulthood, or whatever
word we want to make up, is more noun-y.

+
   // Updates the image view to contain the appropriate button state image.
   void UpdateImage();