GitLab

Add ExtensionsClient::GetUserAgent() for extension related
classes to use instead of querying the ChromeContentClient directly.

Bug: 446329
Change-Id: I3416a14d359ba50bec22d376410a0674d620b67f
Reviewed-on: https://chromium-review.googlesource.com/587403
Commit-Queue: Michael Giuffrida <michaelpg@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491352}