Refactor reifier to make it less dart_codegen specific.

test/dart_codegen/expect/core/iterable.dart

Index: test/dart_codegen/expect/core/iterable.dart
diff --git a/test/dart_codegen/expect/core/iterable.dart b/test/dart_codegen/expect/core/iterable.dart
index 29faf442131e636ffa50d338c4a94f1d370a3405..a212e934aeb8199f8e44f807c72109c7a1bc09d7 100644
--- a/test/dart_codegen/expect/core/iterable.dart
+++ b/test/dart_codegen/expect/core/iterable.dart
@@ -46,9 +46,9 @@ part of dart.core;
  class _GeneratorIterable<E> extends IterableBase<E> implements EfficientLength {final int _start;
  final int _end;
  final _Generator<E> _generator;
- _GeneratorIterable(this._end, E generator(int n)) : _start = 0, _generator = ((__x10) => DEVC$RT.cast(__x10, dynamic, DEVC$RT.type((__t8<E> _) {
+ _GeneratorIterable(this._end, E generator(int n)) : _start = 0, _generator = ((__x8) => DEVC$RT.cast(__x8, dynamic, DEVC$RT.type((_Generator<E> _) {
 }
-), "CompositeCast", """line 320, column 22 of dart:core/iterable.dart: """, __x10 is __t8<E>, false))((generator != null) ? generator : _id);
+), "CompositeCast", """line 320, column 22 of dart:core/iterable.dart: """, __x8 is _Generator<E>, false))((generator != null) ? generator : _id);
  _GeneratorIterable.slice(this._start, this._end, this._generator);
  Iterator<E> get iterator => new _GeneratorIterator<E>(_start, _end, _generator);
  int get length => _end - _start;
@@ -88,4 +88,3 @@ _current = null;
 }
  abstract class BidirectionalIterator<E> implements Iterator<E> {bool movePrevious();
 }
- typedef E __t8<E>(int __u9);