[tools] backport_node.py increments V8 version in target.

tools/release/test_backport_node.py

 #!/usr/bin/env python
 # 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.
 
 import os
 import shutil
 import subprocess
 import sys
 import tempfile
 import unittest
 
+from common_includes import FileToText
 import backport_node
 
 # Base paths.
 BASE_DIR = os.path.dirname(os.path.abspath(__file__))
 TEST_DATA = os.path.join(BASE_DIR, 'testdata')
 
 def gitify(path):
   files = os.listdir(path)
   subprocess.check_call(['git', 'init'], cwd=path)
   subprocess.check_call(['git', 'add'] + files, cwd=path)
@@ skipping 32 matching lines @@
     message = subprocess.check_output(['git', 'log', '-1', '--format=%B'], cwd=node_cwd)
     self.assertIn('Original commit message:\n\n    Title\n\n    Body', message)
 
     # Check patch.
     gitlog = subprocess.check_output(
         ['git', 'diff', 'master', '--cached', '--', 'deps/v8/v8_foo'],
         cwd=node_cwd,
     )
     self.assertIn('+zonk', gitlog.strip())
 
+    # Check version.
+    version_file = os.path.join(node_cwd, "deps", "v8", "include", "v8-version.h")
+    self.assertIn('#define V8_PATCH_LEVEL 4322', FileToText(version_file))
+
 if __name__ == "__main__":
   unittest.main()