One thing we have to do when tracaing is udpate context information (e.g. edge name) if the tracer is a kind that requires it. It's simpler and more efficient to give all tracers this context and perform an unconditional write to the stack.
Mostly we can get away without saving/restoring context information too. This adds AutoClearTracingContext for the one place we need to do this because of nested use of the same tracer while tracing something else.
Differential Revision: https://phabricator.services.mozilla.com/D103500
4234a7dca4