This yak shave went as follows:
Fix https://github.com/flutter/flutter/issues/8795 by adding stocks to
the examples README.
Notice the layers entry in that README isn't quite right either.
Update that.
Check the layers/README file is worth pointing at.
Update the layers/README.
Let's run some of the layer tests to see if they still work.
Oops, need to update them to gradle.
Ok let's try running them again.
Oops, sector is broken.
Add a test for sector.
Fix sector. Find you need to add an assert to a const constructor.
Notice we need to turn const asserts on for the analyzer.
Notice the analysis_options files are out of sync with each other and
with the full list of lints.
Turn on the lints that should be on.
Fix the bugs that finds.
