Rationalize coercions

test/dart_codegen/expect/collection/hash_set.dart

 part of dart.collection;
  abstract class _HashSetBase<E> extends SetBase<E> {Set<E> difference(Set<Object> other) {
   Set<E> result = _newSet();
    for (var element in this) {
-    if (!other.contains(element)) result.add(DEVC$RT.cast(element, dynamic, E, "CastGeneral", """line 17, column 48 of dart:collection/hash_set.dart: """, element is E, false));
+    if (!other.contains(element)) result.add(DEVC$RT.cast(element, dynamic, E, "CompositeCast", """line 17, column 48 of dart:collection/hash_set.dart: """, element is E, false));
     }
    return result;
   }
  Set<E> intersection(Set<Object> other) {
   Set<E> result = _newSet();
    for (var element in this) {
-    if (other.contains(element)) result.add(DEVC$RT.cast(element, dynamic, E, "CastGeneral", """line 25, column 47 of dart:collection/hash_set.dart: """, element is E, false));
+    if (other.contains(element)) result.add(DEVC$RT.cast(element, dynamic, E, "CompositeCast", """line 25, column 47 of dart:collection/hash_set.dart: """, element is E, false));
     }
    return result;
   }
  Set<E> _newSet();
  Set<E> toSet() => _newSet()..addAll(this);
 }
  abstract class HashSet<E> implements Set<E> {external factory HashSet({
 bool equals(E e1, E e2), int hashCode(E e), bool isValidKey(potentialKey)}
 );
  external factory HashSet.identity();
  factory HashSet.from(Iterable elements) {
 HashSet<E> result = new HashSet<E>();
  for (E e in elements) result.add(e);
  return result;
 }
  Iterator<E> get iterator;
 }