Add --last_week/-W option to my_activity.py

Some weeks, writing snippets on Monday just doesn't happen. And during
those weeks, doing date arithmetic then correctly formatting a U.S.
date is too hard.

R=szager@chromium.org, deymo@chromium.org

Review URL: https://codereview.chromium.org/230823003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@262723 0039d316-1c4b-4281-b951-d872f2087c98

my_activity.py

@@ -702,7 +702,7 @@ def main():
                                               relativedelta(months=2))
   parser.add_option(
       '-Q', '--last_quarter', action='store_true',
-      help='Use last quarter\'s dates, e.g. %s to %s' % (
+      help='Use last quarter\'s dates, i.e. %s to %s' % (
         quarter_begin.strftime('%Y-%m-%d'), quarter_end.strftime('%Y-%m-%d')))
   parser.add_option(
       '-Y', '--this_year', action='store_true',
@@ -710,6 +710,9 @@ def main():
   parser.add_option(
       '-w', '--week_of', metavar='<date>',
       help='Show issues for week of the date')
+  parser.add_option(
+      '-W', '--last_week', action='store_true',
+      help='Show last week\'s issues')
   parser.add_option(
       '-a', '--auth',
       action='store_true',
@@ -791,6 +794,8 @@ def main():
       begin, end = get_year_of(datetime.today())
     elif options.week_of:
       begin, end = (get_week_of(datetime.strptime(options.week_of, '%m/%d/%y')))
+    elif options.last_week:
+      begin, end = (get_week_of(datetime.today() - timedelta(days=7)))
     else:
       begin, end = (get_week_of(datetime.today() - timedelta(days=1)))
   else: