[Extensions] Make DeclarativeContent ContentAction's type-agnostic

Make the DeclarativeContent API's ContentActions agnostic to the type
of action the extension has, instead using any action associated with
the extension (whether it's a page action, browser action, or action).

Bug: 893373
Change-Id: I030d7670f314f5359167af7d7dfc3c2ca6164ba8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1564802
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#651082}
3 files changed