Bug 1933428 - Part 3: Recompute partitionKey for top-level documents if required. r=bvandersloot,smaug

The principal of a document might be changed during loading in certain
situation, e.g. a sandboxed document. In this case, we need to recompute
the partitionKey of the document to reflect the change on the principal.

Differential Revision: https://phabricator.services.mozilla.com/D230819

dom/base/Document.h

@@ -4208,6 +4208,12 @@ class Document : public nsINode,
   // the state was changed.
   bool RecomputeResistFingerprinting();
 
+  // Recompute the partitionKey for this document if needed. This is for
+  // handling the case where the principal of the document is changed during the
+  // loading, e.g. a sandboxed document. We only need to recompute for the
+  // top-level content document.
+  void MaybeRecomputePartitionKey();
+
   void RecordCanvasUsage(CanvasUsage& aUsage);
   void RecordFontFingerprinting();