Add Fullscreen Security FAQ to docs/security/

Change-Id: I527eeef1dbfc5bf88e0412d7cd1f7a39ccfb86aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6315931
Reviewed-by: Amy Ressler <[email protected]>
Commit-Queue: Muyao Xu <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1428456}
diff --git a/docs/security/faq.md b/docs/security/faq.md
index f2b116c..260d793 100644
--- a/docs/security/faq.md
+++ b/docs/security/faq.md
@@ -1080,6 +1080,11 @@
 
 See our [Chrome Custom Tabs security FAQ](custom-tabs-faq.md).
 
+<a name="TOC-What-is-the-security-story-for-Fullscreen-"></a>
+### What is the security story for Fullscreen?
+
+See our dedicated [Fullscreen Security FAQ](https://chromium.googlesource.com/chromium/src/+/main/docs/security/fullscreen.md).
+
 <a name="TOC-How-is-security-different-in-Chrome-for-iOS--"></a>
 ### How is security different in Chrome for iOS?