Add some ArgumentError and RangeError constructors that capture more information.

sdk/lib/core/string.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.core;
 
 /**
  * A sequence of characters.
  *
  * A string can be either single or multiline. Single line strings are
@@ skipping 660 matching lines @@
    * Resets the iterator to the rune at the specified index of the string.
    *
    * Setting a negative [rawIndex], or one greater than or equal to
    * [:string.length:],
    * is an error. So is setting it in the middle of a surrogate pair.
    *
    * Setting the position to the end of then string will set [current] to null.
    */
   void set rawIndex(int rawIndex) {
     if (rawIndex >= string.length) {
-      throw new RangeError.range(rawIndex, 0, string.length - 1);
+      throw new RangeError.index(rawIndex, string);
     }
     reset(rawIndex);
     moveNext();
   }
 
   /**
    * Resets the iterator to the given index into the string.
    *
    * After this the [current] value is unset.
    * You must call [moveNext] make the rune at the position current,
@@ skipping 72 matching lines @@
         _position = position - 1;
         _currentCodePoint = _combineSurrogatePair(prevCodeUnit, codeUnit);
         return true;
       }
     }
     _position = position;
     _currentCodePoint = codeUnit;
     return true;
   }
 }