dart2js cps: Use TypeMaskSystem when inserting refinement nodes.

dart2js cps: Use TypeMaskSystem when inserting refinement nodes.

This also fixes a precision bug where checks like 'x is String'
would refine to [subtype=String] instead of [exact=JSString].

R=kmillikin@google.com

Committed: https://github.com/dart-lang/sdk/commit/249a2affaa263c0ce8f275052ab4565eda5d12c4

[asgerf, 2015-09-04 13:53:00]

asgerf@google.com changed reviewers:
+ kmillikin@google.com, sra@google.com

[asgerf, 2015-09-04 13:53:01]

https://codereview.chromium.org/1316673006/diff/1/pkg/compiler/lib/src/cps_ir...
File pkg/compiler/lib/src/cps_ir/type_mask_system.dart (right):

https://codereview.chromium.org/1316673006/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/type_mask_system.dart:24: 
There are two new methods at the end, the rest is just moved to a new file.

https://codereview.chromium.org/1316673006/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/type_mask_system.dart:261: 
The two methods below here are new.

[Kevin Millikin (Google), 2015-09-07 09:02:13]

lgtm

[asgerf, 2015-09-08 14:17:08]

Committed patchset #2 (id:20001) manually as
249a2affaa263c0ce8f275052ab4565eda5d12c4 (presubmit successful).