Removed permission to do `voidExpression is T` and `.. is! T`.

Removed permission to do `voidExpression is T` and `.. is! T`.

The informal spec of generalized void used to allow a `typeTest` on
an expression of type void. This CL removes that permission, thus
leaving only `as` as a narrow escape hatch from void, as decided at the
language team meeting on 2017-08-15.

R=lrn@google.com

Committed: https://github.com/dart-lang/sdk/commit/8514557c5ada0535f6e5d0e0ae854ed20e79ef6b

[eernst, 2017-08-17 09:14:38]

eernst@google.com changed reviewers:
+ lrn@google.com

[Lasse Reichstein Nielsen, 2017-08-17 09:28:38]

lgtm

[eernst, 2017-08-17 09:31:35]

Description was changed from

==========
Removed permission to do `voidExpression is T` and `.. is! T`.

The informal spec of generalized void used to allow a `typeTest` on
an expression of type void. This CL removes that permission, thus
leaving only `as` as a narrow escape hatch from void, as decided at the
language team meeting on 2017-08-15.
==========

to

==========
Removed permission to do `voidExpression is T` and `.. is! T`.

The informal spec of generalized void used to allow a `typeTest` on
an expression of type void. This CL removes that permission, thus
leaving only `as` as a narrow escape hatch from void, as decided at the
language team meeting on 2017-08-15.

R=lrn@google.com

Committed:
https://github.com/dart-lang/sdk/commit/8514557c5ada0535f6e5d0e0ae854ed20e79ef6b
==========

[eernst, 2017-08-17 09:31:36]

Committed patchset #1 (id:1) manually as
8514557c5ada0535f6e5d0e0ae854ed20e79ef6b (presubmit successful).