GitLab

Make discarding the first result possible through Benchmark.ValueCanBeAddedPredicate (add a "is_first_result" arg to it).

The main motivation here is to eliminate special cases for PageTest methods/attributes in user_story_runner.Run.

BUG=440101

Review URL: https://codereview.chromium.org/962793004

Cr-Commit-Position: refs/heads/master@{#319140}