Bug 868396 - Add pref to enable/disable overlay scrollbars on Mac OSX 10.7+. r=smichaud

widget/cocoa/nsLookAndFeel.h

@@ -24,13 +24,13 @@ 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();
 };
 
 #endif // nsLookAndFeel_h_

widget/cocoa/nsNativeThemeCocoa.mm

@@ -2286,13 +2286,15 @@ nsNativeThemeCocoa::DrawWidgetBackground(nsRenderingContext* aContext,
 
     case NS_THEME_SCROLLBAR_SMALL:
     case NS_THEME_SCROLLBAR:
-      if (!nsLookAndFeel::UseOverlayScrollbars()) {
+      if (nsLookAndFeel::GetInt(
+            nsLookAndFeel::eIntID_UseOverlayScrollbars) == 0) {
         DrawScrollbar(cgContext, macRect, aFrame);
       }
       break;
     case NS_THEME_SCROLLBAR_THUMB_VERTICAL:
     case NS_THEME_SCROLLBAR_THUMB_HORIZONTAL:
-      if (nsLookAndFeel::UseOverlayScrollbars()) {
+      if (nsLookAndFeel::GetInt(
+            nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0) {
         BOOL isHorizontal = (aWidgetType == NS_THEME_SCROLLBAR_THUMB_HORIZONTAL);
         BOOL isRolledOver = CheckBooleanAttr(GetParentScrollbarFrame(aFrame),
                                              nsGkAtoms::hover);
@@ -2336,7 +2338,8 @@ nsNativeThemeCocoa::DrawWidgetBackground(nsRenderingContext* aContext,
     break;
     case NS_THEME_SCROLLBAR_TRACK_HORIZONTAL:
     case NS_THEME_SCROLLBAR_TRACK_VERTICAL:
-      if (nsLookAndFeel::UseOverlayScrollbars() &&
+      if (nsLookAndFeel::GetInt(
+            nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0 &&
           CheckBooleanAttr(GetParentScrollbarFrame(aFrame), nsGkAtoms::hover)) {
         BOOL isHorizontal = (aWidgetType == NS_THEME_SCROLLBAR_TRACK_HORIZONTAL);
         const BOOL isOnTopOfBrightBackground = YES; // TODO: detect this properly
@@ -2545,7 +2548,8 @@ nsNativeThemeCocoa::GetWidgetBorder(nsDeviceContext* aContext,
         }
       }
 
-      if (nsLookAndFeel::UseOverlayScrollbars()) {
+      if (nsLookAndFeel::GetInt(
+            nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0) {
         if (isHorizontal) {
           aResult->SizeTo(1, 2, 1, 1);
         } else {
@@ -2802,7 +2806,8 @@ nsNativeThemeCocoa::GetMinimumWidgetSize(nsRenderingContext* aContext,
     {
       *aIsOverridable = false;
 
-      if (nsLookAndFeel::UseOverlayScrollbars()) {
+      if (nsLookAndFeel::GetInt(
+            nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0) {
         aResult->SizeTo(16, 16);
         break;
       }
@@ -3035,7 +3040,8 @@ 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::UseOverlayScrollbars() &&
+      return (nsLookAndFeel::GetInt(
+                nsLookAndFeel::eIntID_UseOverlayScrollbars) == 0 &&
               scrollFrame && scrollFrame->GetScrollbarVisibility());
       break;
     }
@@ -3091,7 +3097,9 @@ nsNativeThemeCocoa::GetWidgetTransparency(nsIFrame* aFrame, uint8_t aWidgetType)
 
   case NS_THEME_SCROLLBAR_SMALL:
   case NS_THEME_SCROLLBAR:
-    return nsLookAndFeel::UseOverlayScrollbars() ? eTransparent : eOpaque;
+    return nsLookAndFeel::GetInt(
+             nsLookAndFeel::eIntID_UseOverlayScrollbars) != 0 ?
+           eTransparent : eOpaque;
 
   case NS_THEME_STATUSBAR:
     // Knowing that scrollbars and statusbars are opaque improves