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This is a reland of crrev.com/c/2573850

This CL adds a new flag parameter supported_features to BackForwardCache
feature. This parameter can specify the set of the features to be
allowed with back-forward cache. This enables us to enable the feature
remotely.

Change-Id: Ib5adce784dc6f0b20d3225a6db5e50fb79167787
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586643
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Fergal Daly <fergal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836993}