* Update comment for accuracy
* Keep the base diff command in a variable; this fixes an oversight where GenerateDiff would run svn diff without the --config-dir hack, and makes later refactoring easy
* Apply review comments from https://codereview.chromium.org/14247007/ to existing code

Review URL: https://chromiumcodereview.appspot.com/14366029

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@195308 0039d316-1c4b-4281-b951-d872f2087c98