[Extensions] Finish freezing schema

BUG=604901
BUG=603725
BUG=591164

Review URL: https://codereview.chromium.org/1906593002

Cr-Commit-Position: refs/heads/master@{#388945}
(cherry picked from commit 5fb2548448bd1b76a59d941b729d7a7f90d53bc8)

Review URL: https://codereview.chromium.org/1936673002 .

Cr-Commit-Position: refs/branch-heads/2704@{#315}
Cr-Branched-From: 6e53600def8f60d8c632fadc70d7c1939ccea347-refs/heads/master@{#386251}
11 files changed