fix #26912, correct handling of op assign

fix #26912, correct handling of op assign

Cleans up some strange things in the code. Now uses TypeSystem.refineBinaryExpressionType, which has some extra handling such as correct understanding of type parameter bounds (in strong mode). Fixed/simplified ErrorVerifier's checking to not look at the wrong type.

R=leafp@google.com

Committed: https://github.com/dart-lang/sdk/commit/232553a2096009a93828368aaf3a9e6d6fc939b6

[Jennifer Messerly, 2016-07-20 22:59:00]

jmesserly@google.com changed reviewers:
+ leafp@google.com

[Jennifer Messerly, 2016-07-20 23:40:29]

Description was changed from

==========
fix #26912, correct handling of op assign

lots of strange things in the code. I unified it with typesystem which already
has correct handling. also fixed ErrorVerifier to not look at the wrong type.
==========

to

==========
fix #26912, correct handling of op assign

Cleans up some strange things in the code. Now uses
TypeSystem.refineBinaryExpressionType, which has some extra handling such as
correct understanding of type parameter bounds (in strong mode).
Fixed/simplified ErrorVerifier's checking to not look at the wrong type.
==========

[Leaf, 2016-07-21 00:04:31]

lgtm.

[Jennifer Messerly, 2016-07-21 00:37:36]

Description was changed from

==========
fix #26912, correct handling of op assign

Cleans up some strange things in the code. Now uses
TypeSystem.refineBinaryExpressionType, which has some extra handling such as
correct understanding of type parameter bounds (in strong mode).
Fixed/simplified ErrorVerifier's checking to not look at the wrong type.
==========

to

==========
fix #26912, correct handling of op assign

Cleans up some strange things in the code. Now uses
TypeSystem.refineBinaryExpressionType, which has some extra handling such as
correct understanding of type parameter bounds (in strong mode).
Fixed/simplified ErrorVerifier's checking to not look at the wrong type.

R=leafp@google.com

Committed:
https://github.com/dart-lang/sdk/commit/232553a2096009a93828368aaf3a9e6d6fc939b6
==========

[Jennifer Messerly, 2016-07-21 00:37:37]

Committed patchset #1 (id:1) manually as
232553a2096009a93828368aaf3a9e6d6fc939b6 (presubmit successful).