Updates the PRESUBMIT.py to allow years from 2011 to the current year.
Since Chromium has moved to this policy, we should too.
Code is copied from /depot_tools/presubmit_canned_checks.py but modified for our purpose.

BUG=
TEST=Tested git cl presubmit with a modified .cc file with the 2011 header and one with the 2012.

Review URL: https://webrtc-codereview.appspot.com/770005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2691 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 7570e4f..6eaa408 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -14,6 +14,10 @@
 
 def _LicenseHeader(input_api):
   """Returns the license header regexp."""
+  # Accept any year number from 2011 to the current year
+  current_year = int(input_api.time.strftime('%Y'))
+  allowed_years = (str(s) for s in reversed(xrange(2011, current_year + 1)))
+  years_re = '(' + '|'.join(allowed_years) + ')'
   license_header = (
       r'.*? Copyright \(c\) %(year)s The WebRTC project authors\. '
         r'All Rights Reserved\.\n'
@@ -25,7 +29,7 @@
       r'.*? in the file PATENTS\.  All contributing project authors may\n'
       r'.*? be found in the AUTHORS file in the root of the source tree\.\n'
   ) % {
-      'year': input_api.time.strftime('%Y'),
+      'year': years_re,
   }
   return license_header