Changes dart2js to warn at reified usage of method type variables.

Changes dart2js to warn at reified usage of method type variables.

This CL changes the response to `x is T`, `x is! T`, `x as T`, and `T`
used as a type expression (say, `foo(T)`) where `T` is a method type
variable: It will now emit a warning in these cases.

Test examples associated with `TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED`
have been activated and corrected, such that this behavior is tested.

As a result 'language/generic_methods_type_expression_test.dart' will
now cause warnings when compiled with `dart2js`.

Note that this does not break any tests, because `dart2js` does not make
the compilation fail when there is a warning (also, the analyzer and the
vm are unaffected because this is about a change to `dart2js`, not a
change to the test file).

R=johnniwinther@google.com

Committed: https://github.com/dart-lang/sdk/commit/acc5f59a99d5d8747459c935e6360ac325606cc6

[eernst, 2016-05-24 14:50:26]

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

[eernst, 2016-05-24 14:50:26]

Implements warnings for cases where the reified usage of a method type variable
is guaranteed to fail at runtime.

[Johnni Winther, 2016-05-25 07:35:50]

lgtm

[eernst, 2016-05-25 08:47:00]

Description was changed from

==========
Changes dart2js to warn at reified usage of method type variables.

This CL changes the response to `x is T`, `x is! T`, `x as T`, and `T`
used as a type expression (say, `foo(T)`) where `T` is a method type
variable: It will now emit a warning in these cases.

Test examples associated with `TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED`
have been activated and corrected, such that this behavior is tested.

As a result 'language/generic_methods_type_expression_test.dart' will
now cause warnings when compiled with `dart2js`.

Note that this does not break any tests, because `dart2js` does not make
the compilation fail when there is a warning (also, the analyzer and the
vm are unaffected because this is about a change to `dart2js`, not a
change to the test file).
==========

to

==========
Changes dart2js to warn at reified usage of method type variables.

This CL changes the response to `x is T`, `x is! T`, `x as T`, and `T`
used as a type expression (say, `foo(T)`) where `T` is a method type
variable: It will now emit a warning in these cases.

Test examples associated with `TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED`
have been activated and corrected, such that this behavior is tested.

As a result 'language/generic_methods_type_expression_test.dart' will
now cause warnings when compiled with `dart2js`.

Note that this does not break any tests, because `dart2js` does not make
the compilation fail when there is a warning (also, the analyzer and the
vm are unaffected because this is about a change to `dart2js`, not a
change to the test file).

R=johnniwinther@google.com

Committed:
https://github.com/dart-lang/sdk/commit/acc5f59a99d5d8747459c935e6360ac325606cc6
==========

[eernst, 2016-05-25 08:47:01]

Committed patchset #1 (id:1) manually as
acc5f59a99d5d8747459c935e6360ac325606cc6 (presubmit successful).