The browser.isSynthetic property is needed by the zoom code to detect when to
apply the correct zoom level. In e10s it is currently only set when a new
document is created which means we don't set it right for history navigation.
This sends it with the Content:LocationChange message which is where it is
needed by the zoom code anyway.
--HG--
extra : rebase_source : 3fe515c161dd036c18fc239af59ac934236eada8
extra : source : 8d5f10959b2c4ae498b4a9a3704a5859038190f5