libsync: Replace inserting tuple into unordered_map in favour of pair. am: 380b2f4fea am: 3500cee3e1 am: 898f852d38 Change-Id: Ic05dbf0be2ccbb524d984b3bde26a6b70c05320a Cr-Mirrored-From: https://chromium.googlesource.com/aosp/platform/system/core Cr-Mirrored-Commit: e911d262dfe105cf990d95fed3e32862a91855a1