Minor optimization in _GrowableList.removeAt.

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 _GrowableList<T> extends ListBase<T> {
 
   void insert(int index, T element) {
     if ((index < 0) || (index > length)) {
       throw new RangeError.range(index, 0, length);
     }
     if (index == this.length) {
       add(element);
       return;
     }
     int oldLength = this.length;
     // We are modifying the length just below the is-check. Without the check
     // Array.copy could throw an exception, leaving the list in a bad state
     // (with a length that has been increased, but without a new element).
     if (index is! int) throw new ArgumentError(index);
     this.length++;
     Lists.copy(this, index, this, index + 1, oldLength - index);
     this[index] = element;
   }
 
   T removeAt(int index) {
     var result = this[index];
     int newLength = this.length - 1;
-    Lists.copy(this, index + 1, this, index, newLength - index);
+    if (index < newLength) {
+      Lists.copy(this, index + 1, this, index, newLength - index);
+    }
     this.length = newLength;
     return result;
   }
 
   bool remove(Object element) {
     for (int i = 0; i < this.length; i++) {
       if (this[i] == element) {
         removeAt(i);
         return true;
       }
@@ skipping 280 matching lines @@
       result._setLength(length);
       return result;
     }
     return growable ? <T>[] : new List<T>(0);
   }
 
   Set<T> toSet() {
     return new Set<T>.from(this);
   }
 }