Auto merge of #28546 - yvt:feat-cow-infra, r=jdm

Implement `Location`'s custom internal methods

This PR partly resurrects #16501 and introduces the use of principals object to associate objects and Realms with origins. Using this infrastructure, this PR implements [the custom internal methods][1] of the `Location` interface, which is "maybe-cross-origin".

Unimplemented/incomplete things:

 - Other maybe-cross-origin interfaces, namely `WindowProxy` and `DissimilarWindowLocation`, aren't implemented correctly yet (causing most test cases of `tests/wpt/web-platform-tests/html/browsers/origin/cross-origin-objects/cross-origin-objects.html` to fail).
     - `WindowProxy`: #28556
 - [The "perform a security check" operation][2] and `Location`'s non-cross-origin properties' relevant `Document` origin checks aren't implemented either (not sure if they are covered by the existing tests).
 - There are a slight deviation from the standard and inefficiency in `CrossOriginGetOwnPropertyHelper`'s current implementation.
     - #28557

[1]: https://html.spec.whatwg.org/multipage/#the-location-interface
[2]: https://html.spec.whatwg.org/multipage/browsers.html#integration-with-idl

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #16243 and make some progress in #2382

---
- [x] There are tests for these changes OR
- [ ] These changes do not require tests because ___

1 files changed, 8 insertions, 0 deletions

diff --git a/components/script/dom/bindings/codegen/Configuration.py b/components/script/dom/bindings/codegen/Configuration.py
index b92f68af3b9..cf6885be265 100644
--- a/components/script/dom/bindings/codegen/Configuration.py
+++ b/components/script/dom/bindings/codegen/Configuration.py
@@ -299,6 +299,9 @@ class Descriptor(DescriptorProvider):
                 if iface:
                     iface.setUserData('hasConcreteDescendant', True)
 
+            if self.isMaybeCrossOriginObject():
+                self.proxy = True
+
             if self.proxy:
                 iface = self.interface
                 while iface.parent:
@@ -404,6 +407,11 @@ class Descriptor(DescriptorProvider):
     def supportsIndexedProperties(self):
         return self.operations['IndexedGetter'] is not None
 
+    def isMaybeCrossOriginObject(self):
+        # If we're isGlobal and have cross-origin members, we're a Window, and
+        # that's not a cross-origin object.  The WindowProxy is.
+        return self.concrete and self.interface.hasCrossOriginMembers and not self.isGlobal()
+
     def hasDescendants(self):
         return (self.interface.getUserData("hasConcreteDescendant", False)
                 or self.interface.getUserData("hasProxyDescendant", False))