Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/1257cd8dde6e
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #19610 from eliperelman/bug-1015405-settings-implement-new-perf-events

Bug 1015405 - implementing new startup loading events and relevant test changes

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https://hg.mozilla.org/integration/gaia-central/rev/b3e78b51a07d
Author: Eli Perelman <eli@eliperelman.com>
Desc: Bug 1015405 - implementing new startup loading events and relevant test changes

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https://hg.mozilla.org/integration/gaia-central/rev/88aa0f2e29f4
Author: dwi2 <dwi2@dwi2.com>
Desc: Merge pull request #19801 from dwi2/bug1016412

Bug 1016412 - Fix intermittent error in async_semaphore_test.js

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https://hg.mozilla.org/integration/gaia-central/rev/f7ed2b83d383
Author: Tzu-Lin Huang <tzhuang@mozilla.com>
Desc: Bug 1016412 - Fix intermittent error in async_semaphore_test.js
Bumping manifests a=b2g-bump