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

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https://hg.mozilla.org/integration/gaia-central/rev/d2dbad943faf
Author: EragonJ <eragonj@eragonj.me>
Desc: Merge pull request #12736 from EragonJ/bug-901852

Bug 901852 - [sms][mms] don't run the time header scheduler if the page ...

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https://hg.mozilla.org/integration/gaia-central/rev/b9681771cba1
Author: EragonJ <eragonj@eragonj.me>
Desc: Bug 901852 - [sms][mms] don't run the time header scheduler if the page is hidden

- call TimeHeaderScheduler at right time
- add related tests