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

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https://hg.mozilla.org/integration/gaia-central/rev/c175a29477e6
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Merge pull request #27080 from takenspc/bug1069612

Bug 1069612 - Switch tabs button is not labeled

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https://hg.mozilla.org/integration/gaia-central/rev/c4cec20479a4
Author: Takeshi Kurosawa <taken.spc@gmail.com>
Desc: Bug 1069612 - Switch tabs button is not labeled

This adds labels to Back and Forward buttons too.

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https://hg.mozilla.org/integration/gaia-central/rev/8d2b9481ca34
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Merge pull request #26972 from ythej/bug_990481

Bug 990481 - [ZTE][OPENC]MMS app allows to attach more contents even whe...

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https://hg.mozilla.org/integration/gaia-central/rev/0eb743971d96
Author: Vishnu Teja <vish.thej@gmail.com>
Desc: Bug 990481 - [ZTE][OPENC]MMS app allows to attach more contents even when the max MMS size is reached r=zasypkin

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "fefe03e2491b19dce99ea51739e93a44d284fee9", 
+    "revision": "c175a29477e68e70142687587844423a75dcf4cc", 
     "repo_path": "integration/gaia-central"
 }