Remove some bogus type promotion code.

Remove some bogus type promotion code.

This code was part of an attempt to prototype some possible extensions
to type promotion to handle `if (x is! Foo)`.  I thought I had
rendered it harmless, but it was having some buggy effects.

Also added a test case demonstrating the problem.

R=scheglov@google.com

Committed: https://github.com/dart-lang/sdk/commit/f9c1cab33ba5f9dbee97d6230fa99fddce5b5603

[Paul Berry, 2017-05-31 20:36:15]

paulberry@google.com changed reviewers:
+ scheglov@google.com

[scheglov, 2017-05-31 20:37:49]

LGTM

[Paul Berry, 2017-05-31 20:40:36]

Description was changed from

==========
Remove some bogus type promotion code.

This code was part of an attempt to prototype some possible extensions
to type promotion to handle `if (x is! Foo)`.  I thought I had
rendered it harmless, but it was having some buggy effects.

Also added a test case demonstrating the problem.
==========

to

==========
Remove some bogus type promotion code.

This code was part of an attempt to prototype some possible extensions
to type promotion to handle `if (x is! Foo)`.  I thought I had
rendered it harmless, but it was having some buggy effects.

Also added a test case demonstrating the problem.

R=scheglov@google.com

Committed:
https://github.com/dart-lang/sdk/commit/f9c1cab33ba5f9dbee97d6230fa99fddce5b5603
==========

[Paul Berry, 2017-05-31 20:40:38]

Committed patchset #1 (id:1) manually as
f9c1cab33ba5f9dbee97d6230fa99fddce5b5603 (presubmit successful).