Simpler generic variables resolution.

Simpler generic variables resolution.

Now there is no need to parse to the node to access all the
generic type variables.

R=johnniwinther@google.com,smok@google.com

Committed: https://code.google.com/p/dart/source/detail?r=10890

[Johnni Winther, 2012-08-17 12:10:07]

lgtm

[Roman, 2012-08-17 12:20:37]

lgtm