Change "brotli-encoding" feature to be enabled by default.

BUG=452335
NOTRY=true
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/1960183002
Cr-Commit-Position: refs/heads/master@{#392369}
(cherry picked from commit e3118678848807c0ea60ab086e3d803cb1913098)

Review-Url: https://codereview.chromium.org/1988233003
Cr-Commit-Position: refs/branch-heads/2704@{#616}
Cr-Branched-From: 6e53600def8f60d8c632fadc70d7c1939ccea347-refs/heads/master@{#386251}