Always set inserted range in List.insertRange.

runtime/lib/growable_array.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.
 
 class GrowableObjectArray<T> implements List<T> {
   factory GrowableObjectArray._uninstantiable() {
     throw const UnsupportedOperationException(
         "GrowableObjectArray can only be allocated by the VM");
   }
 
@@ skipping 31 matching lines @@
     if (start < 0 || start > this.length) {
       throw new IndexOutOfRangeException(start);
     }
     var old_length = this.length;
     this.length = old_length + length;  // Will expand if needed.
     Arrays.copy(this,
                 start,
                 this,
                 start + length,
                 old_length - start);
-    if (initialValue !== null) {
-      for (int i = start; i < start + length; i++) {
-        this[i] = initialValue;
-      }
+    for (int i = start; i < start + length; i++) {
+      this[i] = initialValue;
     }
   }
 
   List<T> getRange(int start, int length) {
     if (length == 0) return [];
     Arrays.rangeCheck(this, start, length);
     List list = new List<T>();
     list.length = length;
     Arrays.copy(this, start, list, 0, length);
     return list;
@@ skipping 163 matching lines @@
   T next() {
     if (!hasNext()) {
       throw const NoMoreElementsException();
     }
     return _array[_pos++];
   }
 
   final GrowableObjectArray<T> _array;
   int _pos;
 }