add rounding-using-doubles methods on SkScalar and SkRect

include/core/SkRect.h

Index: include/core/SkRect.h
diff --git a/include/core/SkRect.h b/include/core/SkRect.h
index 397e4a03eea35775e1b0662e0efabd3d942bfe7a..fd8cb16020fd2359ca7435a71be8376ebe850f9c 100644
--- a/include/core/SkRect.h
+++ b/include/core/SkRect.h
@@ -732,6 +732,24 @@ struct SK_API SkRect {
     }
 
     /**
+     *  Variant of round() that explicitly performs the rounding step (i.e. floor(x + 0.5)) using
+     *  double instead of SkScalar (float). It does this by calling SkDScalarRoundToInt(), which
+     *  may be slower than calling SkScalarRountToInt(), but gives slightly more accurate results.
+     *
+     *  e.g.
+     *      SkScalar x = 0.49999997f;
+     *      int ix = SkScalarRoundToInt(x);
+     *      SkASSERT(0 == ix);  // <--- fails
+     *      ix = SkDScalarRoundToInt(x);
+     *      SkASSERT(0 == ix);  // <--- succeeds
+     */
+    void dround(SkIRect* dst) const {
+        SkASSERT(dst);
+        dst->set(SkDScalarRoundToInt(fLeft), SkDScalarRoundToInt(fTop),
+                 SkDScalarRoundToInt(fRight), SkDScalarRoundToInt(fBottom));
+    }
+
+    /**
      *  Set the dst rectangle by rounding "out" this rectangle, choosing the
      *  SkScalarFloor of top and left, and the SkScalarCeil of right and bottom.
      */