Update AUTHORS file for Facebook organization

We are unblocking contributors from @fb.com and @oculus.com to contribute to Chromium. Our primary contributor group is still specified in our Facebook CLA group and should be consulted before allowing any contributions.

Bug: 
Change-Id: I21ee84a29382f034184d053b77b02c78e6055791
Reviewed-on: https://chromium-review.googlesource.com/558708Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46997}

AUTHORS

@@ -28,6 +28,8 @@ Amazon, Inc <*@amazon.com>
 ST Microelectronics <*@st.com>
 Yandex LLC <*@yandex-team.ru>
 StrongLoop, Inc. <*@strongloop.com>
+Facebook, Inc. <*@fb.com>
+Facebook, Inc. <*@oculus.com>
 
 Aaron Bieber <deftly@gmail.com>
 Abdulla Kamar <abdulla.kamar@gmail.com>