Fix V8 GC metric names.
Fix V8 GC metric names.

We need to replace all '_' characters in the name,
not only the first one.

TBR=eakuefner@chromium.org

Review URL: https://codereview.chromium.org/1919243003

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