How to replicate Chrome Extension having access to google's website (keep, calendar) iframe elements?

Question

I'm trying to replicate a feature of the chrome extension Manganum. It is loading an iframe from google keep and display it in a sidebar (see below image). Upon inspecting, I see that it is doing this through the following code lines:

 <iframe 
   frameborder="0" 
   class="p0zA1" 
   src="chrome-extension://jbfeongihppeenfnaofmdeikahaefljd/modules/frame/index.html?widgetName=keep.google.com"
>
    <iframe src="https://keep.google.com?eventName=2e5c3ab5156c9b9998b36369c94f35b1"></iframe>
</iframe>

Side bar Google Keep chrome extension

It seems like "jbfeongihppeenfnaofmdeikahaefljd" is Manganum's extension id. From what I have read, Manganum seems to be loading an existing resource inside their extension. I'm thinking either:

• Their extension have some permisssions that enable this (from checking, I see that their permissions require: "tabs", "history", "bookmarks", "tabGroups")?
• They have some special deal/permission from google themselves to enable iframe access?

From my research it is not possible to load an iframe for google sites onto a different webpage, but it seems like it is possible for a chrome extension as Manganum is doing it.

Can anyone help me understand how they are doing it?