Introduce mkgrokdump to update tools/v8heapconst.py.

test/default.isolate

 # Copyright 2015 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'variables': {
     'command': [
       '../tools/run-tests.py',
     ],
   },
   'includes': [
     'cctest/cctest.isolate',
     'debugger/debugger.isolate',
     'fuzzer/fuzzer.isolate',
     'inspector/inspector.isolate'
     'intl/intl.isolate',
     'message/message.isolate',
     'mjsunit/mjsunit.isolate',
+    'mkgrokdump/mkgrokdump.isolate',
     'preparser/preparser.isolate',
     'unittests/unittests.isolate',
   ],
 }