And while I'm here, I'm giving SVGDataParser.h a more specific/efficient string
include, to just provide the *forward-decl* of nsAString for this file's
"nsAString&" usage in a function prototype.
Depends on D15231
Differential Revision: https://phabricator.services.mozilla.com/D15232
--HG--
extra : moz-landing-system : lando