Big merge from experimental to bleeding edge.

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 = null]) {
-    if (length == null) {
-      return new _GrowableObjectArray<E>();
-    } else {
-      return new _ObjectArray<E>(length);
+  /* patch */ factory List([int length = 0]) {
+    if (length is! int || length < 0) {
+      throw new ArgumentError("Length must be a positive integer: $length.");
     }
+    _GrowableObjectArray<E> result = new _GrowableObjectArray<E>();
+    result.length = 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.");
+    }
+    _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.");
+    }
+    _GrowableObjectArray<E> result =
+        new _GrowableObjectArray<E>.withCapacity(length < 4 ? 4 : length);
+    if (length != 0) {
+      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;
   }
 }