perf: Add a bidirectionally scrolling variant of tough_scrolling_ad_cases

perf: Add a bidirectionally scrolling variant of tough_scrolling_ad_cases

This patch adds a variant of the tough_scrolling_ad_cases benchmark that
scroll both down and up instead of just scrolling down to the bottom of
the page. This is to simulate a user who only looks at the top part of
the page.

BUG=510398
CQ_EXTRA_TRYBOTS=tryserver.chromium.perf:linux_perf_bisect;tryserver.chromium.perf:mac_perf_bisect;tryserver.chromium.perf:win_perf_bisect;tryserver.chromium.perf:android_nexus5_perf_bisect

Review URL: https://codereview.chromium.org/1303953006

Cr-Commit-Position: refs/heads/master@{#345146}