add roundOut that returns its result

BUG=skia:

Review URL: https://codereview.chromium.org/742663002
diff --git a/src/effects/SkBitmapSource.cpp b/src/effects/SkBitmapSource.cpp
index 0d9315b..1d8078d 100644
--- a/src/effects/SkBitmapSource.cpp
+++ b/src/effects/SkBitmapSource.cpp
@@ -67,9 +67,8 @@
         offset->fX = offset->fY = 0;
         return true;
     }
-    SkIRect dstIRect;
-    dstRect.roundOut(&dstIRect);
 
+    const SkIRect dstIRect = dstRect.roundOut();
     SkAutoTUnref<SkBaseDevice> device(proxy->createDevice(dstIRect.width(), dstIRect.height()));
     if (NULL == device.get()) {
         return false;