Minor cleanup in inferrer folder

Minor cleanup in inferrer folder:
 - divided parts into their own libraries
 - removed TypeMaskSystem (it was not really used except for one method)

R=johnniwinther@google.com, sra@google.com

Committed: https://github.com/dart-lang/sdk/commit/ffce70d0aee73ce3120b1ddfd5bc58407aa16a81

[Siggi Cherem (dart-lang), 2015-12-02 23:11:36]

Patchset #1 (id:1) has been deleted

[Siggi Cherem (dart-lang), 2015-12-03 00:13:28]

Patchset #1 (id:20001) has been deleted

[Siggi Cherem (dart-lang), 2015-12-03 00:15:51]

Description was changed from

==========
Make all inference files explicit libraries
==========

to

==========
Minor cleanup in inferrer folder:
 - divided parts into their own libraries
 - removed TypeMaskSystem (it was not really used except for one method)
==========

[Siggi Cherem (dart-lang), 2015-12-03 00:29:54]

sigmund@google.com changed reviewers:
+ johnniwinther@google.com, sra@google.com

[Siggi Cherem (dart-lang), 2015-12-03 00:29:55]

It might not be worth it since we are planning to change things dramatically in
the inference code, but it's tempting to do more renames and refactorings here
to make this code easier to understand. For example:


- code changes:
  - consider removing some of the engine abstractions (why do we need 3?)
  - rename TypeSystem into InferenceAbstraction
  - rename all graph nodes to something more concise like TINode (Type-inference
node) or INode (inference node), instead of TypeInformation. Similarly TIMap
instead of MapTypeInformation etc.
  - rename SimpleTypeInferenceVisitor => InferenceGraphBuilder 
  - rename InferrerVisitor => AbstractInferenceGraphBuilder
  - merge InferrerVisitor + SimpleTypeInferenceVisitor
  - remove dependency from nodes to engine?


- file organization changes:
  - type_graph_nodes.dart => nodes.dart
  - split out "InferenceEngine"s into engine.dart
  - inferrer_visitor + simple_type_inferrer.dart => builder.dart
  - type_graph_inferrer.dart => inferrer.dart
  - node_tracer.dart => tracer.dart

[sra1, 2015-12-03 01:28:16]

lgtm

[Johnni Winther, 2015-12-03 09:07:45]

lgtm

[Siggi Cherem (dart-lang), 2015-12-04 21:37:10]

Description was changed from

==========
Minor cleanup in inferrer folder:
 - divided parts into their own libraries
 - removed TypeMaskSystem (it was not really used except for one method)
==========

to

==========
Minor cleanup in inferrer folder:
 - divided parts into their own libraries
 - removed TypeMaskSystem (it was not really used except for one method)

R=johnniwinther@google.com, sra@google.com

Committed:
https://github.com/dart-lang/sdk/commit/ffce70d0aee73ce3120b1ddfd5bc58407aa16a81
==========

[Siggi Cherem (dart-lang), 2015-12-04 21:37:11]

Committed patchset #1 (id:40001) manually as
ffce70d0aee73ce3120b1ddfd5bc58407aa16a81 (presubmit successful).