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/tools_webrtc/libs/generate_licenses.py b/tools_webrtc/libs/generate_licenses.py
index 2202188..b8894ed 100755
--- a/tools_webrtc/libs/generate_licenses.py
+++ b/tools_webrtc/libs/generate_licenses.py
@@ -46,6 +46,7 @@
     'guava': ['third_party/guava/LICENSE'],
     'ijar': ['third_party/ijar/LICENSE'],
     'jsoncpp': ['third_party/jsoncpp/LICENSE'],
+    'libaom': ['third_party/libaom/source/libaom/LICENSE'],
     'libc++': ['buildtools/third_party/libc++/trunk/LICENSE.TXT'],
     'libc++abi': ['buildtools/third_party/libc++abi/trunk/LICENSE.TXT'],
     'libevent': ['base/third_party/libevent/LICENSE'],