The srcdoc-iframe contentWindow Proxy returned native window methods
unbound, so iframe.contentWindow.getComputedStyle()/addEventListener()/
setTimeout() ran with the Proxy as `this` and threw "Illegal invocation"
on any page that uses a srcdoc iframe under --launch (FullLaunch). The
sibling matchMedia proxy already bound its methods; this one did not.
Wrap each function in an apply/construct trap that swaps the Proxy
receiver for the real window while passing .prototype/.name/.toString/
identity straight through (a plain .bind() drops .prototype and breaks
instanceof/constructors). Cached in a WeakMap for stable identity.
Verified before/after on a launched stealth browser: getComputedStyle,
addEventListener, setTimeout all OK; .prototype preserved.