Relaxes treatment of method type parameter in `as` expressions.

Relaxes treatment of method type parameter in `as` expressions.

This CL changes the semantics of `dart2js --generic-method-syntax`
generated code for `e as T` where `T` is a method type parameter.

The old behavior was to raise a `TypeError` at runtime when such an
expression was evaluated. The new behavior is to consider `T` as an
alias for `dynamic`, i.e., `e as T` will then always succeed.

Addresses part of issue 27460, omits a part that is not yet agreed upon.

R=johnniwinther@google.com

Committed: https://github.com/dart-lang/sdk/commit/b5d2b38aa3f3704e16ef33af7872188b1568a532

[eernst, 2016-10-03 15:33:44]

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

[eernst, 2016-10-03 15:33:45]

Sdk issue 27460 requests a new semantics for `e as T` where `T` is a formal
method type parameter, namely that it should always be a no-op. Similarly, `e is
T` should always be `true`. This CL implements the former, but omits the latter
(because it is still being discussed).

This CL includes a TODO which was discussed IRL. It just serves as a reminder
about an apparent inconsistency.

[Johnni Winther, 2016-10-04 07:49:35]

lgtm

[eernst, 2016-10-18 09:11:58]

Description was changed from

==========
Relaxes treatment of method type parameter in `as` expressions.

This CL changes the semantics of `dart2js --generic-method-syntax`
generated code for `e as T` where `T` is a method type parameter.

The old behavior was to raise a `TypeError` at runtime when such an
expression was evaluated. The new behavior is to consider `T` as an
alias for `dynamic`, i.e., `e as T` will then always succeed.

Addresses part of issue 27460, omits a part that is not yet agreed upon.
==========

to

==========
Relaxes treatment of method type parameter in `as` expressions.

This CL changes the semantics of `dart2js --generic-method-syntax`
generated code for `e as T` where `T` is a method type parameter.

The old behavior was to raise a `TypeError` at runtime when such an
expression was evaluated. The new behavior is to consider `T` as an
alias for `dynamic`, i.e., `e as T` will then always succeed.

Addresses part of issue 27460, omits a part that is not yet agreed upon.

R=johnniwinther@google.com

Committed:
https://github.com/dart-lang/sdk/commit/b5d2b38aa3f3704e16ef33af7872188b1568a532
==========

[eernst, 2016-10-18 09:11:59]

Committed patchset #2 (id:20001) manually as
b5d2b38aa3f3704e16ef33af7872188b1568a532 (presubmit successful).