Added FLAG_SOURCE_DATA to support additional data that is not supposed to be
part of the default mapping.
Should merged with I1484c2e62788bedb57a42869a5fb25cd8f64482f, otherwize rebuilding
an index may add an extra field to CirrusSearch mapping.
Bug: T134978
Change-Id: Ia41f8eeb9dd4f764543bdd4d71b7a50de8101101