Removing unnecessary warning when parsing Json.

BUG=
R=sigmund@google.com

Review URL: https://codereview.chromium.org//781643002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/source_maps@42098 260f80e4-7a28-3924-810f-c04153c831b5
3 files changed
tree: 66372a35cc604071c42eb832ce5d4967b2a692fb
  1. pkgs/