On our hardy boxes, the python has the json module, but it doesn't
have all the expected methods.  Fallback to simplejson if it
doesn't have json.loads().

Review URL: http://codereview.chromium.org/1520025

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@43907 0039d316-1c4b-4281-b951-d872f2087c98