Introduce mkgrokdump to update tools/v8heapconst.py.

test/mkgrokdump/mkgrokdump.status

Index: test/mkgrokdump/mkgrokdump.status
diff --git a/test/mkgrokdump/mkgrokdump.status b/test/mkgrokdump/mkgrokdump.status
new file mode 100644
index 0000000000000000000000000000000000000000..8fd6a0417ac783b1b4ddc5faf287bb1db6faa71c
--- /dev/null
+++ b/test/mkgrokdump/mkgrokdump.status
@@ -0,0 +1,10 @@
+# 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.
+
+[
+# Only test for default mode x64.
+['variant != default or arch != x64', {
+  '*': [SKIP],
+}],  # variant != default or arch != x64
+]