POC trigger page

This page calls window.print() to invoke PrintRenderFrameHelper::ScriptedPrint in the renderer, where the code-injection patch sends a crafted PrintManagerHost::UpdatePrintSettings IPC with printerType=kLocal and deviceName="\\127.0.0.1\poc-printer".

On a Windows build, watch the browser-process stderr for the [POC] BROWSER PROCESS: SetCrashKeys line proving the renderer-controlled UNC path reached the in-browser ::OpenPrinter call.