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

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https://hg.mozilla.org/integration/gaia-central/rev/d4b273de0b96
Author: Fabien Cazenave <fabien@cazenave.cc>
Desc: Merge pull request #28312 from fabi1cazenave/emergencyCallIcon

Bug 1122688 - missing "Emergency Call" icon, r=drs

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https://hg.mozilla.org/integration/gaia-central/rev/82ddb69e764e
Author: Fabien Cazenave <fabien@cazenave.cc>
Desc: Bug 1122688 - missing "Emergency Call" icon

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https://hg.mozilla.org/integration/gaia-central/rev/e5d8d590f396
Author: Eli Perelman <eli@eliperelman.com>
Desc: Merge pull request #28000 from eliperelman/bug-1129041-verticalhome

Bug 1129041 - Homescreen: remove user timing shim

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https://hg.mozilla.org/integration/gaia-central/rev/d665408e9d2b
Author: Eli Perelman <eli@eliperelman.com>
Desc: Bug 1129041 - Homescreen: remove user timing shim

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "855619b844282e7b941a59d28baaf38ce0284b36", 
+        "git_revision": "a290cd24d46ad8ad3febb1e33b4e4be53913dd6b", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "151a63aae5c5f0a73e98de5e801a866d470b200f", 
+    "revision": "d4b273de0b964c396a621b5fbd575df972b084f7", 
     "repo_path": "integration/gaia-central"
 }