Use maps instead of objects in ElidedTitleCache
Use maps instead of objects in ElidedTitleCache

Properly handles corner case 'constructor' value.

BUG=catapult:#2589

Review-Url: https://codereview.chromium.org/2194103003

sahiljain/catapult,benschmaus/catapult,catapult-project/catapult-csm,benschmaus/catapult,sahiljain/catapult,sahiljain/catapult,catapult-project/catapult,catapult-project/catapult,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult,benschmaus/catapult,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult-csm,sahiljain/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,sahiljain/catapult,sahiljain/catapult,catapult-project/catapult-csm