Optimize latin1-decoder.
Optimize latin1-decoder.

Instead of checking "allowInvalid" inside the innermost loop, create two
different classes.

Speeds up both cases significantly.

BUG= http://dartbug.com/17659
R=ajohnsen@google.com

Review URL: https://codereview.chromium.org//445333004

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@39022 260f80e4-7a28-3924-810f-c04153c831b5

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