How to restrict declarativeNetRequest rule to requests originating from the extension's offscreen page

[Filipp Riabchun]

I'm embedding iframes in my offscreen page.The goal is to have an always-open hidden tab with the corresponding website where I can inject a script to interact with a notification service.

To do that, I need to interfere with the website's CSP. What I used to do with Manifest V2 was

```
browser.webRequest.onHeadersReceived.addListener(
  ({responseHeaders}) => ({
    responseHeaders: responseHeaders
      .filter(header => header.name.toLowerCase() !== 'x-frame-options')
      .map(header =>
        header.name.toLowerCase() === 'content-security-policy'
          ? {
              ...header,
              value: header.value.replace('frame-ancestors', `frame-ancestors ${window.origin} `),
            }
          : header,
      ),
  }),
  {
    urls: ['<all_urls>'],
    types: ['sub_frame'],
  },
  ['blocking', 'responseHeaders', isChrome && 'extraHeaders'].filter(Boolean),
)
```

I'm migrating to V3 and I'm trying to achieve it using

```
browser.declarativeNetRequest.updateDynamicRules({
  removeRuleIds: [1],
  addRules: [
    {
      id: 1,
      priority: 1,
      action: {
        type: 'modifyHeaders',
        responseHeaders: [
          {
            header: 'Content-Security-Policy',
            operation: 'remove',
          },
          {
            header: 'X-Frame-Options',
            operation: 'remove',
          },
        ],
      },
      condition: {
        resourceTypes: ['sub_frame'],
        initiatorDomains: [browser.runtime.id],
      },
    },
  ],
})
```

But looks like the `initiatorDomains` filter doesn't work properly with the requests originating from the offscreen page. Can it be that it works only with http(s):// schema? I don't want to omit the initiator filter because that would mean compromising the website's security