* Add --record-to option to flutter tools
This option will cause flutter tools to record all process
invocations that occur and serialize their stdout and stderr
to files that get added to a "recording" ZIP file. This is
part of an effort to be able to test flutter tools in a hermetic
environment.
As a side-benefit, this recording should prove an excellent
attachment to any bug report.
With this change, they're run via instance methods on an object
obtained through the context. This will allow us to substitute
that object in tests with replay/record versions to allow us to
mock out the os-layer in tests.