Change new List(n) to return fixed length list.

runtime/lib/regexp_patch.dart

Index: runtime/lib/regexp_patch.dart
diff --git a/runtime/lib/regexp_patch.dart b/runtime/lib/regexp_patch.dart
index 2eab296397e89942a61bd75334f9deb5ecdc7692..e365f30e5bb7356b983b7fb503cd1707dc223e4c 100644
--- a/runtime/lib/regexp_patch.dart
+++ b/runtime/lib/regexp_patch.dart
@@ -44,7 +44,7 @@ class _JSRegExpMatch implements Match {
   }
 
   List<String> groups(List<int> groupsSpec) {
-    var groupsList = new List<String>.fixedLength(groupsSpec.length);
+    var groupsList = new List<String>(groupsSpec.length);
     for (int i = 0; i < groupsSpec.length; i++) {
       groupsList[i] = group(groupsSpec[i]);
     }