Improve perf testing framework The ANGLERenderTest subclasses have a parameter "iterations". Previously most of these tests would perform iterations^2 iterations, since the looping was done both in ANGLERenderTest and in the individual test classes. Do the looping only in the individual test classes instead. This enables getting rid of separate beginDrawBenchmark() and endDrawBenchmark() functions. Some other unused code is also removed: 1. stepBenchmark function 2. unused parameters to step() This makes the core loop of running tests simpler. The perf testing framework also now has shared logic for deciding when to end a given test. The score calculation for tests is also changed. Instead of reporting just the number of operations done, it is reported relative to the actual run time of the test. This should make the test results more accurate, since run time of the tests may have some variation. It also enables changing the run time of the tests without rebaselining them. In the tests that use GPU, GPU operations are also waited to finish before stopping the timer. BUG=angleproject:1261 TEST=angle_perftests Change-Id: I69e9aad8afd2d9dedd60e144f0a5d4203618feef Reviewed-on: https://chromium-review.googlesource.com/319381 Tryjob-Request: Olli Etuaho <oetuaho@nvidia.com> Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org>