Add script to look up a user's activity

Found to be particularly helpful in writing snippets.

This tool looks up all activity for a particular user across many
different services. It looks up changes and reviews across various
Rietveld and Gerrit instances and looks up issues in various google code
projects.

Running with no arguments will look up activity of $USER over the
current week (last week on Monday). I.e. the primary use case is for
looking up your activity for writing snippets.

BUG=


Review URL: https://chromiumcodereview.appspot.com/11140010

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@162561 0039d316-1c4b-4281-b951-d872f2087c98