Bumping gaia.json for 4 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/3f9b2319c2b3
Author: Arthur Chen <crh0716@gmail.com>
Desc: Merge pull request #10918 from crh0716/892393

Bug 892393 - Add 1.5x resolution assets r=rexboy

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https://hg.mozilla.org/integration/gaia-central/rev/26f60f2a526d
Author: crh0716 <crh0716@gmail.com>
Desc: Bug 892393 - Add 1.5x resolution assets

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https://hg.mozilla.org/integration/gaia-central/rev/5140f1fbba25
Author: Francisco Borja Salguero Castellano <fbsc@tid.es>
Desc: Merge pull request #10726 from julienw/885278-updatetimeheaders-with-fixedheader

885278 updatetimeheaders with fixedheader

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https://hg.mozilla.org/integration/gaia-central/rev/8b741e315032
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 885278 - [SMS] `updateTimeHeaders' is not working properly with FixedHeader feature. r=borja

* always call refresh in updateTimeHeaders
* expose updateHeaderContent and use it in updateTimeHeaders so that the fixed
  header is changed in the same time than the other headers

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "7530f9702749c29e4b22f4b85fa73e7106eb6288", 
+    "revision": "3f9b2319c2b3b9491a5e7dd525fe3c22cca73490", 
     "repo_path": "/integration/gaia-central"
 }