[pinpoint] Fix Validate() call in /new handler.
[pinpoint] Fix Validate() call in /new handler.

Validate() doesn't return true or false; rather it raises an Exception on
validation failure.

BUG=catapult:#3395, catapult:#3394

Review-Url: https://codereview.chromium.org/2858643003

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