Enables hot-tracking for overflow extension buttons in the app menu

ui/native_theme/native_theme.h

Index: ui/native_theme/native_theme.h
diff --git a/ui/native_theme/native_theme.h b/ui/native_theme/native_theme.h
index b09dd15b1c17171fe6dffbb7aa1f9b100bd4e920..6ba1f04e8dbba5955dccd49ee2c1b07bcc51c199 100644
--- a/ui/native_theme/native_theme.h
+++ b/ui/native_theme/native_theme.h
@@ -132,6 +132,7 @@ class NATIVE_THEME_EXPORT NativeTheme {
 
   struct MenuItemExtraParams {
     bool is_selected;
+    int corner_radius;
   };
 
   struct MenuListExtraParams {
@@ -197,6 +198,8 @@ class NATIVE_THEME_EXPORT NativeTheme {
   };
 
   union ExtraParams {
+    ExtraParams();

[Peter Kasting, 2016/02/18 04:03:43]

Does just using = default work?  Or does the compiler refuse to generate this?

[varkha, 2016/02/18 05:24:48]

No, unfortunately I am still getting uninitialized values if I do (in cc file):
NativeTheme::ExtraParams::ExtraParams() = default;

Unrelated, I am getting style violation if I do "= default" in the header:
../../ui/native_theme/native_theme.h:201:5: error: [chromium-style] Complex
constructor has an inlined body.
    ExtraParams() = default;

I believe "= default" merely creates an empty constructor with an empty
initializer list and an empty body and still does not initialize values.
Definitions here -
http://en.cppreference.com/w/cpp/language/default_initialization

+
     ButtonExtraParams button;
     InnerSpinButtonExtraParams inner_spin;
     MenuArrowExtraParams menu_arrow;