Fix a couple bugs in r42055.

This works around https://github.com/dart-lang/async_await/issues/72,
fixes an incorrect variable name, and updates the async-compiled
output.

R=rnystrom@google.com
TBR

Review URL: https://codereview.chromium.org//766393002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42057 260f80e4-7a28-3924-810f-c04153c831b5