Goal:
Make sure no successful[1] test execution leaves temporary file behind. While Swarming bots (mostly) handle this problem just fine, it's still a pain for developers and just poor hygiene.

[1] This issue isn't about failing tests. There can't be guarantee about a failing test; this is out of scope here.


Background:
Previous efforts already made sure that all tests are runnable from a read only directory ( issue 116251 ) and do not depend on full path. This is an continuation of the test execution self-containment effort. Swarming bots already report the number of temporary files in their TMP directory for maintenance purpose.


Action Items:
- Add TMP files detection in run_isolated.py after a task completes successfully. Report it by injecting this condition in the stdout.
- File bugs and fix any issue discovered.
- Once all problems are detected and fixed, enforce this by also setting exit:255.