Use Analytic AA in SkAAClip

src/core/SkAnalyticEdge.h

Index: src/core/SkAnalyticEdge.h
diff --git a/src/core/SkAnalyticEdge.h b/src/core/SkAnalyticEdge.h
index f4b23ba2b6bd6ab77c5e0b2d0bc5aaeb1d291d96..00812866d5063cc848e42239dea2ba57a4dcd84d 100644
--- a/src/core/SkAnalyticEdge.h
+++ b/src/core/SkAnalyticEdge.h
@@ -43,7 +43,8 @@ struct SkAnalyticEdge {
     static const int kDefaultAccuracy = 2; // default accuracy for snapping
 
     static inline SkFixed snapY(SkFixed y, int accuracy = kDefaultAccuracy) {
-        return SkFixedRoundToFixed(y << accuracy) >> accuracy;
+        // This approach is safer than left shift, round, then right shift
+        return (y + (SK_Fixed1 >> (accuracy + 1))) >> (16 - accuracy) << (16 - accuracy);
     }
 
     // Update fX, fY of this edge so fY = y