Disable Webview Overlay when invisible

Remove Webview overlays when Webview node is set to invisible

Bug: 187292989
Test: play a video in a Webview, toggle visibility for the view, check
existence of a surface control named as "Webview Overlay
SurfaceControl#0"

Change-Id: If47a78a8ae1f7b65b9e7ab983ec72f580d78191a