Put back the unit test on optimizing removeLast to pop. Also don't forget that jsArrayRemoveLast mi…

tests/compiler/dart2js/value_range_test.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.
 
 import 'compiler_helper.dart';
 
 const int REMOVED = 0;
 const int ABOVE_ZERO = 1;
 const int BELOW_LENGTH = 2;
 const int KEPT = 3;
@@ skipping 46 matching lines @@
 }
 """,
 KEPT,
 
 """
 main() {
   var a = new List();
   return a.removeLast();
 }
 """,
-REMOVED, // TODO(6829): Put it back to KEPT
+KEPT,
 
 """
 main() {
   var a = new List(4);
   return a[0];
 }
 """,
 REMOVED,
 
 """
@@ skipping 176 matching lines @@
       break;
   }
 }
 
 
 main() {
   for (int i = 0; i < TESTS.length;  i += 2) {
     expect(TESTS[i], TESTS[i + 1]);
   }
 }