Reland "Fix the fat rect bug in the threaded backend"

This reverts commit 1b637615144604a2d50cf983ac9aa5aab71cf73b.

Reason for revert: add guard flag

Original change's description:
> Revert "Fix the fat rect bug in the threaded backend"
> 
> This reverts commit c41569a29fde10c6fec43cc4593334e9a4b34b76.
> 
> Reason for revert: maybe break the Chrome layout tests
> 
> Original change's description:
> > Fix the fat rect bug in the threaded backend
> > 
> > Bug: skia:7813
> > Change-Id: I954232be1dccc63ce412ccde92c4f0e4617317b9
> > Reviewed-on: https://skia-review.googlesource.com/121641
> > Reviewed-by: Cary Clark <caryclark@google.com>
> > Commit-Queue: Yuqian Li <liyuqian@google.com>
> 
> TBR=caryclark@google.com,liyuqian@google.com,reed@google.com
> 
> Change-Id: If35617a9774b3367561981e39a2fa89a972684b9
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: skia:7813
> Reviewed-on: https://skia-review.googlesource.com/121820
> Reviewed-by: Yuqian Li <liyuqian@google.com>
> Commit-Queue: Yuqian Li <liyuqian@google.com>

TBR=caryclark@google.com,liyuqian@google.com,reed@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: skia:7813
Change-Id: I8b17be4251b5efc20142295cca787474f32e3a86
Reviewed-on: https://skia-review.googlesource.com/122100
Commit-Queue: Yuqian Li <liyuqian@google.com>
Reviewed-by: Yuqian Li <liyuqian@google.com>
diff --git a/src/core/SkScanPriv.h b/src/core/SkScanPriv.h
index 3d36498..f2bb390 100644
--- a/src/core/SkScanPriv.h
+++ b/src/core/SkScanPriv.h
@@ -90,7 +90,11 @@
         return true; // The intersection is empty. Hence consider it done.
     }
     SkIRect bounds = rect.roundOut();
+#ifdef SK_SUPPORT_LEGACY_THREADED_DAA_BUGS
     if (bounds.width() < 3 || bounds.height() < 3) {
+#else
+    if (bounds.width() < 3) {
+#endif
         return false; // not fat
     }
     blitter->blitFatAntiRect(rect);