Append source param to embedded gaia URL

as requested by haon@ for logging purpose

BUG=

Review URL: https://codereview.chromium.org/136793028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246085 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246085