Applying post-commit comments from https://codereview.chromium.org/607993002/

BUG=skia:
R=robertphillips@google.com

Author: junov@chromium.org

Review URL: https://codereview.chromium.org/612063003
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index ad1b4c4..ff03400 100755
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -1575,6 +1575,7 @@
         return;
     }
     ASSERT_OWNED_RESOURCE(src);
+    ASSERT_OWNED_RESOURCE(dst);
 
     SkIRect srcRect = SkIRect::MakeWH(dst->width(), dst->height());
     if (topLeft) {