Rationalize coercions

test/dart_codegen/expect/collection/set.dart

 part of dart.collection;
  abstract class SetMixin<E> implements Set<E> {bool add(E element);
  bool contains(Object element);
  E lookup(E element);
  bool remove(Object element);
  Iterator<E> get iterator;
  Set<E> toSet();
  int get length;
  bool get isEmpty => length == 0;
  bool get isNotEmpty => length != 0;
@@ skipping 56 matching lines @@
   List<E> result = growable ? (new List<E>()..length = length) : new List<E>(length);
    int i = 0;
    for (E element in this) result[i++] = element;
    return result;
   }
  Iterable map(f(E element)) => new EfficientLengthMappedIterable<E, dynamic>(this, f);
  E get single {
   if (length > 1) throw IterableElementError.tooMany();
    Iterator it = iterator;
    if (!it.moveNext()) throw IterableElementError.noElement();
-   E result = DEVC$RT.cast(it.current, dynamic, E, "CastGeneral", """line 130, column 16 of dart:collection/set.dart: """, it.current is E, false);
+   E result = DEVC$RT.cast(it.current, dynamic, E, "CompositeCast", """line 130, column 16 of dart:collection/set.dart: """, it.current is E, false);
    return result;
   }
  String toString() => IterableBase.iterableToFullString(this, '{', '}');
  Iterable<E> where(bool f(E element)) => new WhereIterable<E>(this, f);
  Iterable expand(Iterable f(E element)) => new ExpandIterable<E, dynamic>(this, f);
  void forEach(void f(E element)) {
   for (E element in this) f(element);
   }
  E reduce(E combine(E value, E element)) {
   Iterator<E> iterator = this.iterator;
@@ skipping 51 matching lines @@
   return new SkipIterable<E>(this, n);
   }
  Iterable<E> skipWhile(bool test(E value)) {
   return new SkipWhileIterable<E>(this, test);
   }
  E get first {
   Iterator it = iterator;
    if (!it.moveNext()) {
     throw IterableElementError.noElement();
     }
-   return DEVC$RT.cast(it.current, dynamic, E, "CastGeneral", """line 220, column 12 of dart:collection/set.dart: """, it.current is E, false);
+   return DEVC$RT.cast(it.current, dynamic, E, "CompositeCast", """line 220, column 12 of dart:collection/set.dart: """, it.current is E, false);
   }
  E get last {
   Iterator it = iterator;
    if (!it.moveNext()) {
     throw IterableElementError.noElement();
     }
    E result;
    do {
-    result = DEVC$RT.cast(it.current, dynamic, E, "CastGeneral", """line 230, column 16 of dart:collection/set.dart: """, it.current is E, false);
+    result = DEVC$RT.cast(it.current, dynamic, E, "CompositeCast", """line 230, column 16 of dart:collection/set.dart: """, it.current is E, false);
     }
    while (it.moveNext()); return result;
   }
  E firstWhere(bool test(E value), {
   E orElse()}
 ) {
   for (E element in this) {
     if (test(element)) return element;
     }
    if (orElse != null) return orElse();
@@ skipping 35 matching lines @@
    int elementIndex = 0;
    for (E element in this) {
     if (index == elementIndex) return element;
      elementIndex++;
     }
    throw new RangeError.index(index, this, "index", null, elementIndex);
   }
 }
  abstract class SetBase<E> extends SetMixin<E> {static String setToString(Set set) => IterableBase.iterableToFullString(set, '{', '}');
 }