Specify clip rects when drawing Mac native widgets

Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 117 matching lines @@
         bufferRect.move(-scrollbar->frameRect().x(), -scrollbar->frameRect().y());
 
         imageBuffer = ImageBuffer::create(bufferRect.size());
         if (!imageBuffer)
             return true;
 
         drawingContext = imageBuffer->context();
     }
 
     // Draw thumbless.
-    gfx::SkiaBitLocker bitLocker(drawingContext->canvas());
+    gfx::SkiaBitLocker bitLocker(drawingContext->canvas(), scrollbar->frameRect());
     CGContextRef cgContext = bitLocker.cgContext();
     HIThemeDrawTrack(&trackInfo, 0, cgContext, kHIThemeOrientationNormal);
 
     IntRect tickmarkTrackRect = trackRect(scrollbar, false);
     if (!canDrawDirectly) {
         tickmarkTrackRect.setX(0);
         tickmarkTrackRect.setY(0);
     }
     // The ends are rounded and the thumb doesn't go there.
     tickmarkTrackRect.inflateY(-tickmarkTrackRect.width());
@@ skipping 183 matching lines @@
         return IntRect(scrollbar->x() + startWidth, scrollbar->y(), scrollbar->width() - totalWidth, thickness);
     return IntRect(scrollbar->x(), scrollbar->y() + startWidth, thickness, scrollbar->height() - totalWidth);
 }
 
 int ScrollbarThemeMacNonOverlayAPI::minimumThumbLength(ScrollbarThemeClient* scrollbar)
 {
     return cThumbMinLength[scrollbar->controlSize()];
 }
 
 }