“unlimitedStorage” permission to a <webview> inside a Chrome App

问题

I have a webview inside a Chrome Packaged App and the app has permissions for storage and unlimitedStorage. When I ask for the available storage space from the app It says 8 GB (that It is the whole space available in the device) but when I do it from the web app that the webview loads It says 600 MB aprox.

How can I do to set unlimitedStorage space to the webview?

来源：https://stackoverflow.com/questions/47165546/unlimitedstorage-permission-to-a-webview-inside-a-chrome-app