add roundOut that returns its result

BUG=skia:

Review URL: https://codereview.chromium.org/742663002
diff --git a/src/effects/SkTileImageFilter.cpp b/src/effects/SkTileImageFilter.cpp
index bebf8f0..04c62d0 100644
--- a/src/effects/SkTileImageFilter.cpp
+++ b/src/effects/SkTileImageFilter.cpp
@@ -36,8 +36,7 @@
 
     SkRect dstRect;
     ctx.ctm().mapRect(&dstRect, fDstRect);
-    SkIRect dstIRect;
-    dstRect.roundOut(&dstIRect);
+    const SkIRect dstIRect = dstRect.roundOut();
     int w = dstIRect.width();
     int h = dstIRect.height();
     if (!fSrcRect.width() || !fSrcRect.height() || !w || !h) {