MacViews: Implement Full Keyboard Access.

ui/views/controls/button/button.cc

Index: ui/views/controls/button/button.cc
diff --git a/ui/views/controls/button/button.cc b/ui/views/controls/button/button.cc
index 9f7e5e283c2542c0a24d6d96e2cc6bce7791add6..5d00e0bff00d4690f61febed98f3600cdd4db0f4 100644
--- a/ui/views/controls/button/button.cc
+++ b/ui/views/controls/button/button.cc
@@ -24,6 +24,16 @@ Button::ButtonState Button::GetButtonStateFrom(ui::NativeTheme::State state) {
   return Button::STATE_NORMAL;
 }
 
+// static
+void Button::ConfigureDefaultFocus(Button* button) {
+// On Mac, buttons are focusable only in full keyboard access mode.

[tapted, 2016/05/03 08:08:25]

nit: move this into the #if (then clang-format will indent it - looks weird in
the first column)

[karandeepb, 2016/05/04 01:56:38]

Done.

+#if defined(OS_MACOSX)
+  button->SetFocusBehavior(FocusBehavior::ACCESSIBLE_ONLY);
+#else
+  button->SetFocusBehavior(FocusBehavior::ALWAYS);
+#endif
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Button, public: