Fix style in histogram.html.
Fix style in histogram.html.

BUG=catapult:#3144

Review-Url: https://codereview.chromium.org/2638143002

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