Inconsistency: prerender documents get nonsensical frameId

[bershanskiy]

Description

When document is prerendered, it gets the correct tabId, but its frameId is not correct if it is a top-level document.

Example

The following chrome.runtime.Sender was received on Chrome 112:

{
    "id": "eimadpbcbfnmbkopoojfekhnkhdbieeh",
    "url": "http://example.com/",
    "origin": "http://example.com",
    "frameId": 697,
    "documentId": "26B9995FADB439DA29A5EB8FEDA94D5A",
    "documentLifecycle": "prerender",
    "tab": {
        "active": true,
        "audible": false,
        "autoDiscardable": true,
        "discarded": false,
        "favIconUrl": "",
        "groupId": -1,
        "height": 653,
        "highlighted": true,
        "id": 1013287509,
        "incognito": false,
        "index": 1,
        "mutedInfo": {
            "muted": false
        },
        "openerTabId": 1013287455,
        "pinned": false,
        "selected": true,
        "status": "complete",
        "title": "New Tab",
        "url": "chrome://newtab/",
        "width": 1280,
        "windowId": 1013287454
    }
}

[zombie]

Chrome's doc https://docs.google.com/document/d/1xOe5e8CDU9HM6sazGg6aqvK0iPnptilmwBS9qiZSfkY/edit#heading=h.7n9hkps4a3sr

[oliverdunk]

As discussed in the meeting, I want to confirm if this is a bug or intended behaviour that needs additional documentation.

[tophf]

This is the intended behavior, see https://developer.chrome.com/blog/extension-instantnav/

Extension authors that assume the frameId of the outermost frame is 0 (a previous best practice) may have problems. Since a tab can now have multiple outermost frames (prerendered and cached pages), the assumption that there is a single outermost frame for a tab is incorrect. frameId == 0 will still continue to represent the outermost frame of the active page, but the outermost frames of other pages in the same tab will be non-zero. A new field frameType has been added to fix this problem. See the “How do I determine if a frame is the outermost frame?” section of this post.