add missing template start tag in metric_debugger_app
add missing template start tag in metric_debugger_app

BUG=catapult:#2674

Review-Url: https://codereview.chromium.org/2248453003

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