[RESTRICT AUTOMERGE] Ignore small source rect hint

Which may be abused by malicious app to create a non-visible PiP
window that bypasses the background restriction.

Bug: 270368476
Test: Manually, using the POC app
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:a54d763886ffd69aa14360dc999c76cd2af263f2)
Merged-In: Ifc0e4ffe8b7a9754053246069cb480aa6a59a7e1
Change-Id: Ifc0e4ffe8b7a9754053246069cb480aa6a59a7e1