chrome.storage.local.getBytesInUse polyfill

Currently, Firefox has not implemented the getBytesInUse method for the local storage area. This polyfill fixes that in both chrome and browser namespaces.

Example Usage

require("webext-getBytesInUse-polyfill");

browser.storage.local.set({hello: "there!"})
    .then(browser.storage.local.getBytesInUse("hello"))
    .then((bytes) => console.log("Bytes consumed: " + bytes))
    .error(() => console.log("Storage limit exceeded!"));