Factor out length check in list factories: reduce bloat, factorize code, improve performance.

runtime/lib/array_patch.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.
 
 // Note that the optimizing compiler depends on the algorithm which
 // returns a _GrowableObjectArray if length is null, otherwise returns
 // fixed size array.
 patch class List<E> {
   /* patch */ factory List([int length = 0]) {
     if ((length is! int) || (length < 0)) {
-      throw new ArgumentError("Length must be a positive integer: $length.");
+      _throwArgumentError(length);
     }
-    _GrowableObjectArray<E> result = new _GrowableObjectArray<E>();
-    result.length = length;
+    _GrowableObjectArray<E> result = new _GrowableObjectArray<E>(length);
     return result;
   }
 
   /* patch */ factory List.fixedLength(int length, {E fill: null}) {
     if ((length is! int) || (length < 0)) {
-      throw new ArgumentError("Length must be a positive integer: $length.");
+      _throwArgumentError(length);
     }
     _ObjectArray<E> result = new _ObjectArray<E>(length);
     if (fill != null) {
       for (int i = 0; i < length; i++) {
         result[i] = fill;
       }
     }
     return result;
   }
 
   /* patch */ factory List.filled(int length, E fill) {
     if ((length is! int) || (length < 0)) {
-      throw new ArgumentError("Length must be a positive integer: $length.");
+      _throwArgumentError(length);
     }
     _GrowableObjectArray<E> result =
         new _GrowableObjectArray<E>.withCapacity(length < 4 ? 4 : length);
     result.length = length;
     if (fill != null) {
       for (int i = 0; i < length; i++) {
         result[i] = fill;
       }
     }
     return result;
   }
 
   // Factory constructing a mutable List from a parser generated List literal.
   // [elements] contains elements that are already type checked.
   factory List._fromLiteral(List elements) {
     var list = new List<E>();
     if (elements.length > 0) {
       list._setData(elements);
       list.length = elements.length;
     }
     return list;
   }
+
+  static void _throwArgumentError(int length) {
+    throw new ArgumentError("Length must be a positive integer: $length.");
+  }
 }