[M74] Use dav1d by default

CHERRYPICK
Not able to do a clean cherrypick. These files required manual merge:
  media/media_options.gni
  third_party/libaom/options.gni

This CL turns on dav1d by default. It also disables libaom to save on
binary size.

Bug: 924370
Change-Id: I4d331a3b66fe6031930f5f56880866b9a3c92df8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539901
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Auto-Submit: Thomas Guilbert <tguilbert@chromium.org>
Reviewed-by: Tom Finegan <tomfinegan@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#645600}
(cherry picked from commit ede4345734371ac35b4e50cea7ef3332dabd54d5)

TBR: tomfinegan@chromium.org
Change-Id: I4d331a3b66fe6031930f5f56880866b9a3c92df8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1548047
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/branch-heads/3729@{#590}
Cr-Branched-From: d4a8972e30b604f090aeda5dfff68386ae656267-refs/heads/master@{#638880}
8 files changed