Parser support for trailing commas (#26647).

Parser support for trailing commas (#26647).

Adds parser support for trailing commas in parameter and argument lists.

Meta-tracking issue: https://github.com/dart-lang/sdk/issues/26644

In most cases, errors were preserved (and tested) across parsers with and without the flag set.  (The exception is a formal paramater list with an extra comma, like `(a,,)` which with trailing comma support enabled only reports a missing identifier; needless to say this is captured in a test and is up for further debate.)

Amazingly (and for better or worse), turning this option on in the parser (`parseTrailingCommas = true`) produces NO errors in the analyzer and server tests.

BUG=26647
R=brianwilkerson@google.com

Committed: https://github.com/dart-lang/sdk/commit/aea4632375d9cbedff2b3ce87dd8b46b1e2645be

[pquitslund, 2016-07-01 20:18:28]

Description was changed from

==========
Parser support for trailing commas (#26644).

Adds parser support for trailing commas in parameter and argument lists.

Tracking issue: https://github.com/dart-lang/sdk/issues/26644

In most cases, errors were preserved (and tested) across parsers with and
without the flag set.  (The exception is a formal paramater list with an extra
comma, like `(a,,)` which with trailing comma support enabled only reports a
missing identifier; needless to say this is captured in a test and is up for
further debate.)

Amazingly (and for better or worse), turning this option on in the parser
(`parseTrailingCommas = true`) produces NO errors in the analyzer and server
tests.

BUG=26644
==========

to

==========
Parser support for trailing commas (#26647).

Adds parser support for trailing commas in parameter and argument lists.

Meta-tracking issue: https://github.com/dart-lang/sdk/issues/26644

In most cases, errors were preserved (and tested) across parsers with and
without the flag set.  (The exception is a formal paramater list with an extra
comma, like `(a,,)` which with trailing comma support enabled only reports a
missing identifier; needless to say this is captured in a test and is up for
further debate.)

Amazingly (and for better or worse), turning this option on in the parser
(`parseTrailingCommas = true`) produces NO errors in the analyzer and server
tests.

BUG=26647
==========

[pquitslund, 2016-07-01 20:18:38]

pquitslund@google.com changed reviewers:
+ brianwilkerson@google.com

[Brian Wilkerson, 2016-07-01 20:40:08]

lgtm. I'm surprised (and bothered) by the fact that there were no completion
failures.

[pquitslund, 2016-07-01 20:50:13]

Description was changed from

==========
Parser support for trailing commas (#26647).

Adds parser support for trailing commas in parameter and argument lists.

Meta-tracking issue: https://github.com/dart-lang/sdk/issues/26644

In most cases, errors were preserved (and tested) across parsers with and
without the flag set.  (The exception is a formal paramater list with an extra
comma, like `(a,,)` which with trailing comma support enabled only reports a
missing identifier; needless to say this is captured in a test and is up for
further debate.)

Amazingly (and for better or worse), turning this option on in the parser
(`parseTrailingCommas = true`) produces NO errors in the analyzer and server
tests.

BUG=26647
==========

to

==========
Parser support for trailing commas (#26647).

Adds parser support for trailing commas in parameter and argument lists.

Meta-tracking issue: https://github.com/dart-lang/sdk/issues/26644

In most cases, errors were preserved (and tested) across parsers with and
without the flag set.  (The exception is a formal paramater list with an extra
comma, like `(a,,)` which with trailing comma support enabled only reports a
missing identifier; needless to say this is captured in a test and is up for
further debate.)

Amazingly (and for better or worse), turning this option on in the parser
(`parseTrailingCommas = true`) produces NO errors in the analyzer and server
tests.

BUG=26647
R=brianwilkerson@google.com

Committed:
https://github.com/dart-lang/sdk/commit/aea4632375d9cbedff2b3ce87dd8b46b1e2645be
==========

[pquitslund, 2016-07-01 20:50:15]

Committed patchset #1 (id:1) manually as
aea4632375d9cbedff2b3ce87dd8b46b1e2645be (presubmit successful).