Bug 313498 – [Site Isolation] Document::isSecureContext ignores RemoteFrame ancestors

• Component: New Bugs
• Status: RESOLVED FIXED

[Anthony Tarbinian]

In Document::isSecureContext, WebKit walks the frame tree to check
if all of a frame's ancestors are "secure". It does this to gate access to
powerful web APIs such as navigator.geolocation.

For each ancestor, we call Document::isDocumentSecure which performs
checks to see if the frame is potentially trustworthy. Below is the implementation.
It does the following:
1. If the document is sandboxed, it checks if the document's URL is trustworthy 
2. Otherwise, check if the document's security origin is trustworthy.

```
static inline bool isDocumentSecure(const Document& document)
{
     if (document.isSandboxed(SandboxFlag::Origin))   
         return isURLPotentiallyTrustworthy(document.url());
     return document.securityOrigin().isPotentiallyTrustworthy();
}
```

With site isolation enabled, it is possible for some of the document's
ancestors to be RemoteFrames in different processes. Currently, the
code in Document::isSecureContext, only handles LocalFrames and silently
skips any RemoteFrame ancestors.

This bug causes imported/w3c/web-platform-tests/secure-contexts/basic-popup-and-iframe-tests.html
to fail with site isolation enabled.

[Radar WebKit Bug Importer]

<rdar://problem/175714384>

[EWS]

Committed 312199@main (e211768ca32e): <https://commits.webkit.org/312199@main>

Reviewed commits have been landed. Closing PR #63753 and removing active labels.