Improve the speed and memory efficiency of csslib parsing.

Improve the speed and memory efficiency of csslib parsing.

In particular, this avoids calling [FileSpan.start] and [FileSpan.end]
where possible, since they lazily instantiate objects.

R=sra@google.com

Committed: https://code.google.com/p/dart/source/detail?r=42080

[nweiz, 2014-11-22 01:04:04]

nweiz@google.com changed reviewers:
+ terry@google.com

[sra1, 2014-12-02 23:43:45]

sra@google.com changed reviewers:
+ sra@google.com

[sra1, 2014-12-02 23:43:45]

lgtm (if parser.dart:2383 is not a bug.)

Maybe it would read a bit better if var start was renamed to firstSpan.

https://codereview.chromium.org/751453004/diff/1/pkg/csslib/lib/parser.dart
File pkg/csslib/lib/parser.dart (right):

https://codereview.chromium.org/751453004/diff/1/pkg/csslib/lib/parser.dart#n...
pkg/csslib/lib/parser.dart:2383: start = _peekToken.span;
Will the _peekToken always have a span starting immediately following the
skipped quote?

[nweiz, 2014-12-03 00:21:15]

Committed patchset #1 (id:1) manually as 42080 (presubmit successful).

[terry, 2014-12-04 14:21:18]

lgtm sorry I missed this in all my mail during the holiday.