Rationalize coercions

Rationalize coercions

This breaks out casts / coercions into:

Standard (on by default)
- DynamicCasts: dynamic -> T
- AssignmentCasts: T x = expr; // T must be a ground type

Inference (this will go away)
- InferableLiteral
- InferableClosure
- InferableAllocation

Implicit (no flag yet, but i'll add to disable by default)
- DownCastComposite: Any cast to a non-ground type
- DownCastImplicit: Any other implicit downcast not covered above

A flag is also added to enable/disable all wrapping.  This is not off by default yet, but that is the intent.

R=leafp@google.com

Committed: https://github.com/dart-lang/dev_compiler/commit/f7a51364a7bdf28d013b2fdf26b4e036c2d18ded

[vsm, 2015-03-25 19:32:52]

vsm@google.com changed reviewers:
+ leafp@google.com, sigmund@google.com

[Leaf, 2015-03-25 21:06:28]

lgtm

https://codereview.chromium.org/1038583004/diff/1/lib/src/checker/rules.dart
File lib/src/checker/rules.dart (right):

https://codereview.chromium.org/1038583004/diff/1/lib/src/checker/rules.dart#...
lib/src/checker/rules.dart:459: // FIXME(vsm): I don't think we need this any
more.
Why not?

https://codereview.chromium.org/1038583004/diff/1/lib/src/info.dart
File lib/src/info.dart (right):

https://codereview.chromium.org/1038583004/diff/1/lib/src/info.dart#newcode229
lib/src/info.dart:229: return new InferableLiteral(rules, expression, cast);
We'll need to split out the inferable literals from the non-inferable literals
at some point.

https://codereview.chromium.org/1038583004/diff/1/lib/src/info.dart#newcode334
lib/src/info.dart:334: // generics.
I think this comment is orphaned?

https://codereview.chromium.org/1038583004/diff/1/test/checker/checker_test.dart
File test/checker/checker_test.dart (right):

https://codereview.chromium.org/1038583004/diff/1/test/checker/checker_test.d...
test/checker/checker_test.dart:96: x = /*warning:InferableLiteral*/null;
This should really be a cast.

[vsm, 2015-03-25 21:52:03]

Committed patchset #3 (id:40001) manually as
f7a51364a7bdf28d013b2fdf26b4e036c2d18ded (presubmit successful).