Rename pref/settings for media autoplay scope to be Web Application Scope.

This is also removing a feature flag that is no longer needed.

Bug: 923910
Change-Id: I45dde867148e1eee92178bd398a356c6acdcbf24
Reviewed-on: https://chromium-review.googlesource.com/c/1425857
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Auto-Submit: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#625932}(cherry picked from commit 5fa01ee9445401038f074d8f39e8c0792fc694bb)
Reviewed-on: https://chromium-review.googlesource.com/c/1450403
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/branch-heads/3683@{#131}
Cr-Branched-From: e51029943e0a38dd794b73caaf6373d5496ae783-refs/heads/master@{#625896}
13 files changed