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

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https://hg.mozilla.org/integration/gaia-central/rev/acd16d8eeb4d
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #18793 from julienw/995116-attachment-reduce-memory

Bug 995116 - [Tarako][MMS][Gallery] SMS/MMS OOM after attach a large pix...

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https://hg.mozilla.org/integration/gaia-central/rev/2df1e1f48a21
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 995116 - [Tarako][MMS][Gallery] SMS/MMS OOM after attach a large pixel picture from gallery r=azasypkin

This patch does the following changes:

* we use -moz-samplesize to decode the images to resize them
* we try to free data more aggressively by using setTimeout

(Original patch from Steve Schung, then modified)
Bumping manifests a=b2g-bump