[DIP] Restrict DocumentIsolationPolicy to secure contexts
This CL ensures that DocumentIsolationPolicy is only taken into account
in secure contexts. It also moves the gating of DocumentIsolationPolicy
on the feature flag from header parsing to before the
PolicyContainerHost policies are computed, in order to have just one
place where DIP headers are reset to their default values.
Bug: 341022370
Change-Id: Ib46c8e47fe421bcf97663f41c4209988c253cfb1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5598773
Reviewed-by: Tsuyoshi Horo horo@chromium.org
Reviewed-by: Joe DeBlasio jdeblasio@chromium.org
Commit-Queue: Camille Lamy clamy@chromium.org
Cr-Commit-Position: refs/heads/main@{#1317866}