GitLab

New tests:
- Added new ChromeProxyExplicitBypass integration tests that test "bypass=0", "bypass=<X>", "block=0", and "block=<X>" Chrome-Proxy directives using the test server
- Added new ChromeProxyFallback integration test that gets a "bypass=0" directive from the real data reduction proxy

Cleanup:
- Rewrote the VerifyBadProxies logic, adding support for per-proxy retry times
- Also changed VerifyBadProxies to raise an exception instead of returning false when the actual and expected bad proxy lists were different, which was causing all the existing bypass tests to pass in cases when they should have failed
- Fixed typo in ChromeProxyCorsBypass test, it passes now
- Some general python style cleanup

BUG=374397

Review URL: https://codereview.chromium.org/659333004

Cr-Commit-Position: refs/heads/master@{#300295}