[scheduler] Rename DisableBackForwardCache scheduling policy.

Rename DisableBackForwardCache to RecordMetricsForBackForwardCache as we
don't yet have a back-forward cache to opt out from.

R=kinuko@chromium.org
CC=​haraken@chromium.org
BUG=933147

Change-Id: Ia189926bcf24790cb5c055fce48d4d2b91362fc8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1571697
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652221}
15 files changed