move synthetic fasta closers into the token stream

move synthetic fasta closers into the token stream

* add new SyntheticSymbolToken class

* whenever fasta inserts a closer ( '}', ']', ')' ) that is not part
  of the original source, ensure that the inserted closer is
  synthetic (isSynthetic returns true) and in the token stream

* make EOF a synthetic token

R=ahe@google.com, scheglov@google.com

Committed: https://github.com/dart-lang/sdk/commit/4a783d14654219b97d0e0698a50a7f539302084b

[danrubel, 2017-03-27 13:47:39]

danrubel@google.com changed reviewers:
+ ahe@google.com, scheglov@google.com

[scheglov, 2017-03-27 14:00:07]

lgtm

[ahe, 2017-03-27 14:13:50]

lgtm

Don't forget to run dart2js unit tests on this, in particular
tests/compiler/dart2js/message_kind_test.dart.

This test should complain if dart2js starts to generate additional message after
this change.

[danrubel, 2017-03-29 19:02:18]

Description was changed from

==========
move synthetic fasta closers into the token stream

* add new SyntheticSymbolToken class

* whenever fasta inserts a closer ( '}', ']', ')' ) that is not part
  of the original source, ensure that the inserted closer is
  synthetic (isSynthetic returns true) and in the token stream

* make EOF a synthetic token
==========

to

==========
move synthetic fasta closers into the token stream

* add new SyntheticSymbolToken class

* whenever fasta inserts a closer ( '}', ']', ')' ) that is not part
  of the original source, ensure that the inserted closer is
  synthetic (isSynthetic returns true) and in the token stream

* make EOF a synthetic token

R=ahe@google.com, scheglov@google.com

Committed:
https://github.com/dart-lang/sdk/commit/4a783d14654219b97d0e0698a50a7f539302084b
==========

[danrubel, 2017-03-29 19:02:19]

Committed patchset #4 (id:60001) manually as
4a783d14654219b97d0e0698a50a7f539302084b (presubmit successful).