Always initialize Trace
Always initialize Trace

Summary: For convenience, `TRACE(X, 0, ...)` should work without `TRACE=...`.

Reviewed By: Feng23

Differential Revision: D28144389

fbshipit-source-id: e412a50b012d14a482640d88e67c0affb3603844

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex