libwebm/README.libaom: add Chromium required fields

+ make License more specific to match the allow list

Bug: 421989026
Fixed: 421989026
Change-Id: I0a15826634ec6f5081188c8c93948eefb18c8600

third_party/libwebm/README.libaom

diff --git a/third_party/libwebm/README.libaom b/third_party/libwebm/README.libaom
index 6e43487..bc7dbb9 100644
--- a/third_party/libwebm/README.libaom
+++ b/third_party/libwebm/README.libaom
@@ -1,7 +1,10 @@
+Name: libwebm
 URL: https://chromium.googlesource.com/webm/libwebm
 Version: 3b630045052e1e4d563207ab9e3be8d137c26067
-License: BSD
+License: BSD-3-Clause
 License File: LICENSE.TXT
+Shipped in Chromium: no
+Security Critical: yes
 
 Description:
 libwebm is used to handle WebM container I/O.