Optimize List.toList/.sublist and List.from on lists.

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.
 
 // The _GrowableArrayMarker class is used to signal to the List() factory
 // whether a parameter was passed.
 class _GrowableArrayMarker implements int {
   const _GrowableArrayMarker();
 }
 
@@ skipping 14 matching lines @@
     // of new _List.
     var result = new _List<E>(length);
     if (fill != null) {
       for (int i = 0; i < length; i++) {
         result[i] = fill;
       }
     }
     return result;
   }
 
+  /* patch */ factory List.from(Iterable other, { bool growable: true }) {
+    if (other is EfficientLength) {
+      int length = other.length;
+      var list = growable ? new _GrowableList<E>(length) : new _List<E>(length);
+      int i = 0;
+      for (var element in other) { list[i++] = element; }
+      return list;
+    }
+    List<E> list = new _GrowableList<E>(0);
+    for (E e in other) {
+      list.add(e);
+    }
+    if (growable) return list;
+    return makeListFixedLength(list);
+  }
+
   // Factory constructing a mutable List from a parser generated List literal.
   // [elements] contains elements that are already type checked.
   factory List._fromLiteral(List elements) {
     if (elements.isEmpty) {
       return new _GrowableList<E>(0);
     }
     var result = new _GrowableList<E>.withData(elements);
     result._setLength(elements.length);
     return result;
   }
 }