Make smi.toString() do its work faster using native string helpers.
Make smi.toString() do its work faster using native string helpers.

BUG= http://dartbug.com/13450
R=fschneider@google.com

Review URL: https://codereview.chromium.org//24359002

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@27808 260f80e4-7a28-3924-810f-c04153c831b5

dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk