* changes to add firefox as one of the browser options to test_platform and test_runner
* Creating a supported_browsers file to put all the different browser related maps and utilities
* Remove accidentaly forgotten commented out lines. Clear imports
* fix error in screenshot handler
* Addressing PR comments.
* addressing PR comments part 2:
* Add Firefox installing functionality to test platform. For Linux only. Refactor test platform code
* remove download.dart. Not complete for now
* uncomment firefox.dart. Adding new CL parameters.
* Licence headers added.
* adding more comments to firefox_installer
* adding test for firefox download
* address pr comments. change directory for test in .cirrus.yml
* change directory for test_web_engine_firefox_script
* removing the system test.
1. Various functionalities offered by this tool are now organized into commands (e.g. `felt test`, `felt check-licenses`).
2. The felt tool can now be invoked from anywhere, not necessarily from the web_ui directory.
3. This new structure helps us scale better as we add more commands (e.g. soon a `build/watch` command is coming).
- Add a custom `PlatformPlugin` that spins up a server waiting for test to request a screenshot.
- When a screenshot is requested the plugin talks to Chrome via the debug port, captures a screenshot, and compares it with a golden file
- This PR also adds proper CLI for `dev/test.dart` with an `ArgParser` for future extension into a proper developer tool for the team.
- As a first couple of features, it adds `--debug` option to launch Chrome in debug mode, a `--target` option to choose a single test to run rather than all tests, and `--shard` option to choose a subset of tests to run.
Limitations:
- While screenshot test will run on Cirrus, they are configured to not fail on Cirrus. Need to solve Chrome version skew.
- Stack maps do not work yet (you get stacks, but they are nonsensical)
- When requesting a single test, build_runner builds all tests anyway
- Nothing but desktop Chrome is supported
- Nothing but Linux is supported
- There's no Chrome version pinning; currently assumed stable Chrome channel
