Parser fix for lambdas

Parser fix for lambdas. All the heavy lifting courtesy of Stephen :) 
(http://codereview.chromium.org/8400017/)

Only difference in this version is using a List instead of a Map (due to Maps having not so great performance at the moment when the keys are numbers. And we could get even better perf by tweaking this to cache the lookahead on the Token, if we really wanted to)

Committed: https://code.google.com/p/dart/source/detail?r=1683

[Jennifer Messerly, 2011-11-19 01:41:25]

tbr