Rationalize coercions

test/dart_codegen/expect/collection/list.dart

 part of dart.collection;
  abstract class ListBase<E> extends Object with ListMixin<E> {static String listToString(List list) => IterableBase.iterableToFullString(list, '[', ']');
 }
  abstract class ListMixin<E> implements List<E> {Iterator<E> get iterator => new ListIterator<E>(this);
  E elementAt(int index) => this[index];
  void forEach(void action(E element)) {
 int length = this.length;
  for (int i = 0; i < length; i++) {
   action(this[i]);
    if (length != this.length) {
@@ skipping 259 matching lines @@
 RangeError.checkValidRange(start, end, this.length);
  int length = end - start;
  if (length == 0) return; RangeError.checkNotNegative(skipCount, "skipCount");
  List otherList;
  int otherStart;
  if (iterable is List) {
   otherList = DEVC$RT.cast(iterable, DEVC$RT.type((Iterable<E> _) {
     }
   ), DEVC$RT.type((List<dynamic> _) {
     }
-  ), "CastGeneral", """line 369, column 19 of dart:collection/list.dart: """, iterable is List<dynamic>, true);
+  ), "ImplicitCast", """line 369, column 19 of dart:collection/list.dart: """, iterable is List<dynamic>, true);
    otherStart = skipCount;
   }
  else {
   otherList = iterable.skip(skipCount).toList(growable: false);
    otherStart = 0;
   }
  if (otherStart + length > otherList.length) {
   throw IterableElementError.tooFew();
   }
  if (otherStart < start) {
   for (int i = length - 1; i >= 0; i--) {
-    this[start + i] = ((__x11) => DEVC$RT.cast(__x11, dynamic, E, "CastGeneral", """line 381, column 27 of dart:collection/list.dart: """, __x11 is E, false))(otherList[otherStart + i]);
+    this[start + i] = ((__x11) => DEVC$RT.cast(__x11, dynamic, E, "CompositeCast", """line 381, column 27 of dart:collection/list.dart: """, __x11 is E, false))(otherList[otherStart + i]);
     }
   }
  else {
   for (int i = 0; i < length; i++) {
-    this[start + i] = ((__x12) => DEVC$RT.cast(__x12, dynamic, E, "CastGeneral", """line 385, column 27 of dart:collection/list.dart: """, __x12 is E, false))(otherList[otherStart + i]);
+    this[start + i] = ((__x12) => DEVC$RT.cast(__x12, dynamic, E, "CompositeCast", """line 385, column 27 of dart:collection/list.dart: """, __x12 is E, false))(otherList[otherStart + i]);
     }
   }
 }
  void replaceRange(int start, int end, Iterable<E> newContents) {
 RangeError.checkValidRange(start, end, this.length);
  if (newContents is! EfficientLength) {
   newContents = newContents.toList();
   }
  int removeLength = end - start;
  int insertLength = newContents.length;
@@ skipping 81 matching lines @@
   }
  else {
   for (E element in iterable) {
     this[index++] = element;
     }
   }
 }
  Iterable<E> get reversed => new ReversedListIterable<E>(this);
  String toString() => IterableBase.iterableToFullString(this, '[', ']');
 }