dart2js: Bugfix for when 'await' occurs in an initializer list.

dart2js: Bugfix for when 'await' occurs in an initializer list.

If the JS ast contains an initializer list:

  var x = foo(), y = await x;

It would be retained as a single statement and generate invalid output
that awaits 'x' before it has been defined.

CLOSES=23997

BUG=
R=sigurdm@google.com

Committed: https://github.com/dart-lang/sdk/commit/3634c3998a3efb85adfb1a388517a78b87aca208

[asgerf, 2015-10-27 10:10:05]

asgerf@google.com changed reviewers:
+ karlklose@google.com, sigurdm@google.com

[sigurdm, 2015-10-27 10:32:26]

LGTM

Thanks!

[asgerf, 2015-10-27 10:37:02]

Committed patchset #1 (id:1) manually as
3634c3998a3efb85adfb1a388517a78b87aca208 (presubmit successful).