[Web Install] Unrestricted Variant for WebExtensions

Currently, WebExtensions are not able to programmatically install PWAs.

They can however, generate a shortcut using chrome.management.generateAppForLink(URL, title), which was introduced prior to the introduction of Web manifests. It uses the "management" permission. Unfortunately, this API doesn't consider the manifest or its contained preferences.

This situation is not ideal, and unfortunately investment in the extensions platform has always been inadequate. But this API presents an opportunity to also improve extensions.

While the regular version of this API would be usable in extensions, a few changes would bring major improvements. These are centered around relaxing the permissions model.

• extension "management" permission should automatically grant this API's permission
• user gesture and foreground requirements should be waived
• confirmation dialog should be skipped
• getInstalledApps() should return all PWAs regardless of how they were installed
• anything else I missed