RequestContext changes to facilitate thread tracing
RequestContext changes to facilitate thread tracing

Summary: In order to trigger trace points when a new thread begins/finishes executing, I added functionality to call onSet and onUnset methods on all RequestData objects whenever setContext is called. The main question: will this approach cost us too much overhead?

Reviewed By: djwatson

Differential Revision: D3604948

fbshipit-source-id: 3b704ca0f2b713458427aa49be12f776939057f8

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