Test Runner: Determine slow tests from test expectations. This updates the test harness to handle slow test based on the TIMEOUT test expectation. It removes the "registerSlowTests" API in favor of using the test expectation files. Also updates some of the timeout handling for various angle tests, including on SwiftShader for multithreading tests. Increases the timeout for tests in a batch to attempt to fix the problem of the first test being much slower. Bug: angleproject:6261 Change-Id: I7427344da5a0c1ea26d8c2d6eb0e9be2557b56e6 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3104007 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>