Jason Simmons 48de25e19b Do not modify the set of active streams within the embedder tracing callbacks (#2600)
Dart invokes Start/StopTracing callbacks within the _setVMTimelineFlags service
method whenever the embedder timeline stream toggles on or off.  Flutter's
implementation of these callbacks was modifying the set of enabled streams,
which could override the intended behavior of _setVMTimelineFlags.

Start/StopTracing will now only control Flutter's embedder-specific log.

Also needed to change the Flutter engine's --trace-startup flag to set the
corresponding timeline stream flag on the Dart VM.
2016-04-19 10:38:22 -07:00
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