Specify clip rects when drawing Mac native widgets

Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm

Index: Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm
diff --git a/Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm b/Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm
index 0649932408f3a3ce4060b9fcc4530d5954d07a13..d63ab2d11f4797dae6b787daa86a76f4112e618e 100644
--- a/Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm
+++ b/Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm
@@ -33,6 +33,7 @@
 
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/ImageBuffer.h"
+#include "platform/mac/ThemeMac.h"
 #include "platform/scroll/ScrollbarThemeClient.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebRect.h"
@@ -135,7 +136,7 @@ bool ScrollbarThemeMacNonOverlayAPI::paint(ScrollbarThemeClient* scrollbar, Grap
     }
 
     // Draw thumbless.
-    gfx::SkiaBitLocker bitLocker(drawingContext->canvas());
+    gfx::SkiaBitLocker bitLocker(drawingContext->canvas(), ThemeMac::inflateRectForAA(scrollbar->frameRect()));
     CGContextRef cgContext = bitLocker.cgContext();
     HIThemeDrawTrack(&trackInfo, 0, cgContext, kHIThemeOrientationNormal);