Fix overflow:overlay scrollbar width for paint.

third_party/WebKit/Source/platform/scroll/ScrollTypes.h

Index: third_party/WebKit/Source/platform/scroll/ScrollTypes.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollTypes.h b/third_party/WebKit/Source/platform/scroll/ScrollTypes.h
index 32d22c8071fd1e62bd29df498131f24396e2de42..b7e117f52d75a3fef92b7556d8eac4f0cb375d42 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollTypes.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollTypes.h
@@ -43,8 +43,12 @@ inline ScrollOffset toScrollOffset(const FloatPoint& p) {
   return ScrollOffset(p.x(), p.y());
 }
 
+// Platform overlay scrollbars are controlled and painted by the operating
+// system (e.g., OSX and Android).  CSS overlay scrollbars are created by
+// setting overflow:overlay, and they are painted by chromium.
 enum OverlayScrollbarClipBehavior {
-  IgnoreOverlayScrollbarSize,
+  IgnorePlatformOverlayScrollbarSize,
+  IgnorePlatformAndCSSOverlayScrollbarSize,
   ExcludeOverlayScrollbarSizeForHitTesting
 };