Slight cleanup of file locations in flutter_tools
to make it easier to see which files are responsible
for data reporting.

* don't send crash reports if on a user branch.
* add test to test/crash_reporting_test.dart

This modifies our flutter_tools crash reports to include the error
message. This error message may contain personally identifying
information (PII), such as a file system path on the developer's
local machine that may contain user names, project code names,
etc. To disable crash reporting, the developer can run the
following command:

    flutter config --no-analytics

For more information on what gets reported during crashes of the
flutter tool, see:

https://github.com/flutter/flutter/wiki/Flutter-CLI-crash-reporting

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* enable crash reporting in flutter_tools

* fix analytics text; use relative paths

* fix test

- [x] Don't use package:stack_trace.
- [x] Don't use Chain.capture.
- [x] Fix an instance of aggressive catching of exceptions

Related #8742

* add crash reporting without enabling it

* do not drop futures on the floor

* return exitCode from executable run

* debug travis

* remove unnecessary todo

* rename local fs getter