This allows the runtime feature to be overridden by the default state
of the base::Feature.

Note: Fledge base::Feature is not enabled by default yet, therefore we
leave the behavior unchanged for now.

Shared Storage API I2S: https://groups.google.com/a/chromium.org/g/blink-dev/c/dZ0NRwh7cvs/m/RHvbZNp_AgAJ

Fenced Frames I2S: https://groups.google.com/a/chromium.org/g/blink-dev/c/tpw8wW0VenQ/m/mePLTiHlDQAJ

Topics API I2S: https://groups.google.com/a/chromium.org/g/blink-dev/c/PN_aE-X-f9U/m/SweKUn3lBAAJ

Private Aggregation API I2S: https://groups.google.com/a/chromium.org/g/blink-dev/c/8cKaLstq2QQ/m/JENzsATUBgAJ

List of items that are different between I2S and the current implementation:
1. WICG/fenced-frame#155
2. WICG/shared-storage#154
3. https://issues.chromium.org/issues/337055574

Bug: 331926920
Change-Id: I5d2706fabbc6f771d50adfdf358d6daca3322223
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5420588
Reviewed-by: Domenic Denicola <[email protected]>
Reviewed-by: Andrew Verge <[email protected]>
Reviewed-by: Richard (Torne) Coles <[email protected]>
Commit-Queue: Nan Lin <[email protected]>
Reviewed-by: Dominic Farolino <[email protected]>
Reviewed-by: Yao Xiao <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1298072}