Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/b9f776785774
Author: Jan Jongboom <janjongboom@gmail.com>
Desc: Merge pull request #16399 from comoyo/972276

Bug 972276 - Cache window size on event to avoid reflows. r=RudyLu

========

https://hg.mozilla.org/integration/gaia-central/rev/9c74b74b6be3
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 972276 - Cache window size on event to avoid reflows
Bumping manifests a=b2g-bump