Introduce mkgrokdump to update tools/v8heapconst.py.

test/mkgrokdump/mkgrokdump.isolate

Index: test/mkgrokdump/mkgrokdump.isolate
diff --git a/test/mkgrokdump/mkgrokdump.isolate b/test/mkgrokdump/mkgrokdump.isolate
new file mode 100644
index 0000000000000000000000000000000000000000..98faf9de6a7b9dc3e285bf45fbeb6f45d10b4d8e
--- /dev/null
+++ b/test/mkgrokdump/mkgrokdump.isolate
@@ -0,0 +1,16 @@
+# Copyright 2017 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': {
+    'files': [
+      './mkgrokdump.status',
+      './testcfg.py',
+      '../../tools/v8heapconst.py',
+    ],
+  },
+  'includes': [
+    '../../src/base.isolate',
+    '../../tools/testrunner/testrunner.isolate',
+  ],
+}