This prevents multiple simultaneous runs of the analyzer from stomping
over each other (e.g. multiple runs of 'update-packages'). Certain
long-lived commands (like analyze, run, logs) are exempted once they've
done enough work to be safe from most stomping action.
This still doesn't make us entirely safe from craziness, e.g. if you're
half way through an 'update-packages' run and you call 'git pull', who
knows what state you'll end up in. But there's only so much one can do.
Fixes https://github.com/flutter/flutter/issues/2762
* rename service_protocol.dart to protocol_discovery.dart
* add a wrapper around the obs. protocol
* use json-rpc in run
* consolidate obs. code; implement flutter run --benchmark
* review comments
* add google analytics
* send in the run target type
* track device type targets
* use the real GA code
* review comments
* rev to usage 2.0
* rev to 2.2.0 of usage; add tests
* review comments
* more terse flutter upgrade
* fix an issue when updating and the engine update code has changed
* call flutter precache; add a --no-color hidden option
* fix a lint related to getters/setters
