Typecheck constructor initializers properly

test/dart_codegen/expect/core/errors.dart

 part of dart.core;
  class Error {Error();
  static String safeToString(Object object) {
   if (object is num || object is bool || null == object) {
     return object.toString();
     }
    if (object is String) {
     return _stringToSafeString(object);
     }
    return _objectToString(object);
@@ skipping 80 matching lines @@
 explanation = ": Valid value range is empty";
 }
  else {
 explanation = ": Only valid value is $start";
 }
  return "RangeError: $message ($value)$explanation";
 }
 }
  class IndexError extends ArgumentError implements RangeError {final indexable;
  final int length;
- IndexError(int invalidValue, indexable, [String name, String message, int length]) : this.indexable = indexable, this.length = (length != null) ? length : indexable.length, super.value(invalidValue, name, (message != null) ? message : "Index out of range");
+ IndexError(int invalidValue, indexable, [String name, String message, int length]) : this.indexable = indexable, this.length = ((__x3) => DDC$RT.cast(__x3, dynamic, int, "CastGeneral", """line 371, column 23 of dart:core/errors.dart: """, __x3 is int, true))((length != null) ? length : indexable.length), super.value(invalidValue, name, (message != null) ? message : "Index out of range");
  int get start => 0;
  int get end => length - 1;
  String toString() {
 assert (_hasValue); String target = Error.safeToString(indexable);
  var explanation = "index should be less than $length";
  if (invalidValue < 0) {
 explanation = "index must not be negative";
 }
  return "RangeError: $message ($target[$invalidValue]): $explanation";
 }
@@ skipping 39 matching lines @@
  StackTrace get stackTrace => null;
 }
  class StackOverflowError implements Error {const StackOverflowError();
  String toString() => "Stack Overflow";
  StackTrace get stackTrace => null;
 }
  class CyclicInitializationError extends Error {final String variableName;
  CyclicInitializationError([this.variableName]);
  String toString() => variableName == null ? "Reading static variable during its initialization" : "Reading static variable '$variableName' during its initialization";
 }