Re-enable WEBRTC_SVNREVISION script

Message:
Another try to enable the script to get svn revision number. Most code borrowed from
lastchange.py, I simplified and modified to make it work with webrtc. The bottom line
of this script is 1. not breake any existing builds 2. get correct svn revision number
in a typical engineering setup, so it doesn't deal with some corner cases that lastchange.py
does, just simply returns "n/a" since these corner cases will most likely not happen, and
it also make this script simple.

Description:
This script runs "svn info" or "git svn info" to get svn revision number returns "n/a" if
both fail.

BUG=
TEST=try bots
Review URL: https://webrtc-codereview.appspot.com/671004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2502 4adac7df-926f-26a2-2b94-8c16560cd09d

src/build/common.gypi

@@ -99,16 +99,7 @@
       '..','../..', # common_types.h, typedefs.h
     ],
     'defines': [
-      # TODO(leozwang): Temporally disable it because we cannot assume svn
-      # is installed by default, it will break Chromium build. The problem
-      # could happen on Gentoo which download and build tar ball directly,
-      # it also could happen when developer downloads Chromium tar ball and
-      # build inside source tree without svn installed. The solution is to
-      # have a script to deal with these cases and support git-svn.
-      # Two similar issues have been filed at
-      # WebRTC http://code.google.com/p/webrtc/issues/detail?id=496
-      # Chromium http://code.google.com/p/chromium/issues/detail?id=126452
-      'WEBRTC_SVNREVISION="n/a"',
+      'WEBRTC_SVNREVISION="<!(python <(webrtc_root)/build/version.py)"',
     ],
     'conditions': [
       ['build_with_chromium==1', {

src/build/version.py

@@ -0,0 +1,61 @@
+#!/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".
+This script is a simplified version of lastchange.py which is in Chromium's
+src/build/util folder.
+"""
+
+import os
+import subprocess
+import sys
+
+def popen_cmd_and_get_output(cmd, directory):
+  """Return (status, output) of executing cmd in a shell."""
+  try:
+    proc = subprocess.Popen(cmd,
+                            stdout=subprocess.PIPE,
+                            stderr=subprocess.PIPE,
+                            cwd=directory,
+                            shell=(sys.platform=='win32'))
+  except OSError:
+    # command is apparently either not installed or not executable.
+    return None
+  if not proc:
+    return None
+
+  for line in proc.stdout:
+    line = line.strip()
+    if not line:
+      continue
+    words = line.split()
+    for index, word in enumerate(words):
+      if word == "Revision:":
+        return words[index+1]
+  # return None if cannot find keyword Revision
+  return None
+
+def main():
+  directory = os.path.dirname(sys.argv[0]);
+  version = popen_cmd_and_get_output(['git', 'svn', 'info'], directory)
+  if version == None:
+    version = popen_cmd_and_get_output(['svn', 'info'], directory)
+    if version == None:
+      print "n/a"
+      return 0
+  print version
+  return 0
+
+if __name__ == '__main__':
+  sys.exit(main())