Summary:
Changelog: [internal]
To avoid unnecessary string copy in event pipeline, use move semantics.
Event pipeline has ownership of event type. Passing it by reference ends up in a copy when `RawEvent` object is constructed. To avoid this, pass string by value through each layer and use move semantics to avoid extra copies.
Reviewed By: javache
Differential Revision: D34392608
fbshipit-source-id: c11d221be345665e165d9edbc360ba5a057e3890