Move _fatal from dart:core to dart:_internal

Move _fatal from dart:core to dart:_internal

_fatal was a private function in dart:core which was called from a
different library (dart:async).  It's not clear how it was supposed to
work or if it even did.  The uses in dart:async don't appear to be
covered by tests.

Move it to dart:_internal which exists exactly for sharing things
between the dart: libraries.

BUG=
R=kustermann@google.com

Committed: https://github.com/dart-lang/sdk/commit/fdb4c100e0914677fd274b0deff91e6c818a6878

[Kevin Millikin (Google), 2017-02-09 11:41:30]

kmillikin@google.com changed reviewers:
+ kustermann@google.com

[kustermann, 2017-02-09 11:43:18]

LGTM, thanks!

[Kevin Millikin (Google), 2017-02-09 11:46:57]

Description was changed from

==========
Move _fatal from dart:core to dart:_internal

_fatal was a private function in dart:core which was called from a
different library (dart:async).  It's not clear how it was supposed to
work or if it even did.  The uses in dart:async don't appear to be
covered by tests.

Move it to dart:_internal which exists exactly for sharing things
between the dart: libraries.

BUG=
==========

to

==========
Move _fatal from dart:core to dart:_internal

_fatal was a private function in dart:core which was called from a
different library (dart:async).  It's not clear how it was supposed to
work or if it even did.  The uses in dart:async don't appear to be
covered by tests.

Move it to dart:_internal which exists exactly for sharing things
between the dart: libraries.

BUG=
R=kustermann@google.com

Committed:
https://github.com/dart-lang/sdk/commit/fdb4c100e0914677fd274b0deff91e6c818a6878
==========

[Kevin Millikin (Google), 2017-02-09 11:46:59]

Committed patchset #1 (id:1) manually as
fdb4c100e0914677fd274b0deff91e6c818a6878 (presubmit successful).