Remove const interfaces from content/public/common.

Bug: 908139
Tbr: boliu@chromium.org, lazyboy@chromium.org, scottmg@chromium.org, johannes@chromium.org, seantopping@chromium.org
Change-Id: I56fafc55cdb6e77f479c6d657be8dd20162cd2b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1667790
Commit-Queue: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672186}
25 files changed