Bug 880753: Add public nsLookAndFeel::UseOverlayScrollbars method. r=smichaud

widget/cocoa/nsLookAndFeel.h

@@ -24,13 +24,15 @@ public:
     return 0x2022;
   }
 
+  static bool UseOverlayScrollbars();
+
 protected:
 
   // Apple hasn't defined a constant for scollbars with two arrows on each end, so we'll use this one.
   static const int kThemeScrollBarArrowsBoth = 2;
   static const int kThemeScrollBarArrowsUpperLeft = 3;
 
-  static bool UseOverlayScrollbars();
+  static bool SystemWantsOverlayScrollbars();
   static bool AllowOverlayScrollbarsOverlap();
 };
 

widget/cocoa/nsLookAndFeel.mm

@@ -353,7 +353,7 @@ nsLookAndFeel::GetIntImpl(IntID aID, int32_t &aResult)
       aResult = eScrollThumbStyle_Proportional;
       break;
     case eIntID_UseOverlayScrollbars:
-      aResult = UseOverlayScrollbars() ? 1 : 0;
+      aResult = SystemWantsOverlayScrollbars() ? 1 : 0;
       break;
     case eIntID_AllowOverlayScrollbarsOverlap:
       aResult = AllowOverlayScrollbarsOverlap() ? 1 : 0;
@@ -471,6 +471,11 @@ nsLookAndFeel::GetFloatImpl(FloatID aID, float &aResult)
 }
 
 bool nsLookAndFeel::UseOverlayScrollbars()
+{
+  return GetInt(eIntID_UseOverlayScrollbars) != 0;
+}
+
+bool nsLookAndFeel::SystemWantsOverlayScrollbars()
 {
   return ([NSScroller respondsToSelector:@selector(preferredScrollerStyle)] &&
           [NSScroller preferredScrollerStyle] == mozNSScrollerStyleOverlay);

widget/cocoa/nsNativeThemeCocoa.mm

@@ -2321,15 +2321,13 @@ nsNativeThemeCocoa::DrawWidgetBackground(nsRenderingContext* aContext,
 
     case NS_THEME_SCROLLBAR_SMALL:
     case NS_THEME_SCROLLBAR:
-      if (nsLookAndFeel::GetInt(
-            nsLookAndFeel::eIntID_UseOverlayScrollbars) == 0) {
+      if (!nsLookAndFeel::UseOverlayScrollbars()) {
         DrawScrollbar(cgContext, macRect, aFrame);
       }
       break;
     case NS_THEME_SCROLLBAR_THUMB_VERTICAL:
     case NS_THEME_SCROLLBAR_THUMB_HORIZONTAL:
-      if (nsLookAndFeel::GetInt(
-            nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0) {
+      if (nsLookAndFeel::UseOverlayScrollbars()) {
         BOOL isHorizontal = (aWidgetType == NS_THEME_SCROLLBAR_THUMB_HORIZONTAL);
         BOOL isRolledOver = CheckBooleanAttr(GetParentScrollbarFrame(aFrame),
                                              nsGkAtoms::hover);
@@ -2373,8 +2371,7 @@ nsNativeThemeCocoa::DrawWidgetBackground(nsRenderingContext* aContext,
     break;
     case NS_THEME_SCROLLBAR_TRACK_HORIZONTAL:
     case NS_THEME_SCROLLBAR_TRACK_VERTICAL:
-      if (nsLookAndFeel::GetInt(
-            nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0 &&
+      if (nsLookAndFeel::UseOverlayScrollbars() &&
           CheckBooleanAttr(GetParentScrollbarFrame(aFrame), nsGkAtoms::hover)) {
         BOOL isHorizontal = (aWidgetType == NS_THEME_SCROLLBAR_TRACK_HORIZONTAL);
         const BOOL isOnTopOfDarkBackground = IsDarkBackground(aFrame);
@@ -2583,8 +2580,7 @@ nsNativeThemeCocoa::GetWidgetBorder(nsDeviceContext* aContext,
         }
       }
 
-      if (nsLookAndFeel::GetInt(
-            nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0) {
+      if (nsLookAndFeel::UseOverlayScrollbars()) {
         if (isHorizontal) {
           aResult->SizeTo(2, 1, 1, 1);
         } else {
@@ -2841,8 +2837,7 @@ nsNativeThemeCocoa::GetMinimumWidgetSize(nsRenderingContext* aContext,
     {
       *aIsOverridable = false;
 
-      if (nsLookAndFeel::GetInt(
-            nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0) {
+      if (nsLookAndFeel::UseOverlayScrollbars()) {
         aResult->SizeTo(16, 16);
         break;
       }
@@ -3100,8 +3095,7 @@ nsNativeThemeCocoa::ThemeSupportsWidget(nsPresContext* aPresContext, nsIFrame* a
       // overriden, and the custom transparent resizer looks better when
       // scrollbars are not present.
       nsIScrollableFrame* scrollFrame = do_QueryFrame(parentFrame);
-      return (nsLookAndFeel::GetInt(
-                nsLookAndFeel::eIntID_UseOverlayScrollbars) == 0 &&
+      return (!nsLookAndFeel::UseOverlayScrollbars() &&
               scrollFrame && scrollFrame->GetScrollbarVisibility());
       break;
     }
@@ -3157,9 +3151,7 @@ nsNativeThemeCocoa::GetWidgetTransparency(nsIFrame* aFrame, uint8_t aWidgetType)
 
   case NS_THEME_SCROLLBAR_SMALL:
   case NS_THEME_SCROLLBAR:
-    return nsLookAndFeel::GetInt(
-             nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0 ?
-           eTransparent : eOpaque;
+    return nsLookAndFeel::UseOverlayScrollbars() ? eTransparent : eOpaque;
 
   case NS_THEME_STATUSBAR:
     // Knowing that scrollbars and statusbars are opaque improves