Add Av1 Decoder wrapper behind a build flag

Bug: webrtc:11404
Change-Id: I090ffd173d667e8845de1b986af462516b7c76e6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169452
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Michael Horowitz <mhoro@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30757}
diff --git a/DEPS b/DEPS
index a8bd168..c22ac35 100644
--- a/DEPS
+++ b/DEPS
@@ -1,5 +1,8 @@
 # This file contains dependencies for WebRTC.
 
+gclient_gn_args_file = 'src/build/config/gclient_args.gni'
+gclient_gn_args = []
+
 vars = {
   # By default, we should check out everything needed to run on the main
   # chromium waterfalls. More info at: crbug.com/570091.
@@ -192,6 +195,8 @@
     'https://chromium.googlesource.com/chromium/deps/libjpeg_turbo.git@ce0e57e8e636f5132fe6f0590a4dba91f92fd935',
   'src/third_party/libsrtp':
     'https://chromium.googlesource.com/chromium/deps/libsrtp.git@650611720ecc23e0e6b32b0e3100f8b4df91696c',
+  'src/third_party/libaom/source/libaom':
+    'https://aomedia.googlesource.com/aom.git@f83d681765cd2aefa9a70ce771af48edd1dbf416',
   'src/third_party/libvpx/source/libvpx':
     'https://chromium.googlesource.com/webm/libvpx.git@5532775efe808cb0942e7b99bf2f232c6ce99fee',
   'src/third_party/libyuv':