Introduce mkgrokdump to update tools/v8heapconst.py.

test/mkgrokdump/mkgrokdump.gyp

Index: test/mkgrokdump/mkgrokdump.gyp
diff --git a/test/mkgrokdump/mkgrokdump.gyp b/test/mkgrokdump/mkgrokdump.gyp
new file mode 100644
index 0000000000000000000000000000000000000000..17919680bf8236560ca3289b75c4d0a8444193f3
--- /dev/null
+++ b/test/mkgrokdump/mkgrokdump.gyp
@@ -0,0 +1,26 @@
+# 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.
+
+{
+  'conditions': [
+    ['test_isolation_mode != "noop"', {
+      'targets': [
+        {
+          'target_name': 'mkgrokdump_run',
+          'type': 'none',
+          'dependencies': [
+            '../../tools/mkgrokdump.gyp:mkgrokdump',
+          ],
+          'includes': [
+            '../../gypfiles/features.gypi',
+            '../../gypfiles/isolate.gypi',
+          ],
+          'sources': [
+            'mkgrokdump.isolate',
+          ],
+        },
+      ],
+    }],
+  ],
+}