BubbleFrameView: add padding if platform dislikes close buttons

ui/views/widget/widget_delegate.cc

Index: ui/views/widget/widget_delegate.cc
diff --git a/ui/views/widget/widget_delegate.cc b/ui/views/widget/widget_delegate.cc
index c5f9d97490c457d01995bd827481638c33a2b275..50dddcac0d63bcd3dc19e43d7d8d85ac0c898a0d 100644
--- a/ui/views/widget/widget_delegate.cc
+++ b/ui/views/widget/widget_delegate.cc
@@ -79,11 +79,7 @@ bool WidgetDelegate::ShouldShowWindowTitle() const {
 }
 
 bool WidgetDelegate::ShouldShowCloseButton() const {
-#if defined(OS_MACOSX)
-  return false;

[msw, 2016/07/28 19:18:46]

Hmm, now it occurs to me that this might cause the close button to show on any
Mac dialogs that don't use BubbleFrameView... I'm not sure if any Mac dialog
windows use other frames... you might want to try asking around/auditing, taking
a look at DialogDelegate::CreateNonClientFrameView/GetDialogWidgetInitParams and
maybe adding DCHECK[s] there to ensure Mac only ever makes dialog frames with
bubble frame views (or trying to hide other frames' close buttons...).

-#else
   return true;
-#endif
 }
 
 bool WidgetDelegate::ShouldHandleSystemCommands() const {