Re-enable embedding svn revision into code

Description:
By using a python scription, this cl tries to get svn revision properly. It
current support git-svn and svn, if it fails, "n/a" will be defined as
svn revision.


BUG=500
TEST= test cases: w/o svn, w/o git-svn. test platforms, linux/windows. Passed all trybots.
Review URL: https://webrtc-codereview.appspot.com/564010

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2243 4adac7df-926f-26a2-2b94-8c16560cd09d

src/build/common.gypi

@@ -94,9 +94,7 @@
       '..','../..', # common_types.h, typedefs.h
     ],
     'defines': [
-      #'WEBRTC_SVNREVISION="n/a"',
-      #'WEBRTC_SVNREVISION="<(webrtc_version)"',
-      'WEBRTC_SVNREVISION="<!(python <(DEPTH)/src/build/version.py)"',
+      'WEBRTC_SVNREVISION="<!(python <(webrtc_root)/build/version.py)"',
     ],
     'conditions': [
       ['build_with_chromium==1', {

src/build/version.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python
+
+# Copyright (c) 2012 The WebRTC 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 in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS.  All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+"""Get svn revision of working copy
+
+This script tries to get the svn revision as much as it can. It supports
+both git-svn and svn. It will fail if not in a git-svn or svn repository;
+in this case the script will return "n/a".
+"""
+
+__author__ = 'leozwang@webrtc.org (Leo Wang)'
+
+import shlex
+import sys
+
+def popen_cmd_and_get_output(cmd):
+  """Return (status, output) of executing cmd in a shell."""
+  import subprocess
+
+  pipe = subprocess.Popen(shlex.split(cmd),
+                          stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+  stdout, stderr = pipe.communicate()
+  return pipe.returncode, stdout
+
+def get_git_svn_revision(line):
+  """Return revision number in git-svn output, set to "n/a" if it fails."""
+  words = line.split()
+  for index, word in enumerate(words):
+    if word == "Revision:":
+      return words[index+1]
+  return "n/a"
+
+if __name__ == '__main__':
+  (gitstatus, gitresult) = popen_cmd_and_get_output("git svn info")
+  if gitstatus == 0:
+    result = get_git_svn_revision(gitresult)
+    print result
+  else:
+    (svnstatus, svnresult) = popen_cmd_and_get_output("svnversion")
+    if svnstatus == 0:
+      print svnresult
+    else:
+      print "n/a"
+
+  sys.exit(0)