Electron: Extension tab APIs operate across session boundaries

Electron is a framework for writing cross-platform desktop applications using JavaScript, HTML and CSS. Prior to 39.8.8, 40.9.0, 41.2.1, and 42.0.0-beta.3, extension tab and scripting APIs were not scoped to the extension's own session. A malicious or compromised extension loaded into one session could navigate, script, and read from windows belonging to a different session. Apps are only affected if they load Chrome extensions via session.loadExtension and rely on separate sessions to isolate that extension from other content. This issue is fixed in versions 39.8.8, 40.9.0, 41.2.1, and 42.0.0-beta.3.