Bug 1301123 - Add assertions ensuring that documents and inner windows cannot end up with an expanded principal; r=bholley

dom/base/nsNodeInfoManager.cpp

@@ -11,6 +11,7 @@
 #include "nsNodeInfoManager.h"
 
 #include "mozilla/DebugOnly.h"
+#include "mozilla/Telemetry.h"
 #include "mozilla/dom/NodeInfo.h"
 #include "mozilla/dom/NodeInfoInlines.h"
 #include "nsCOMPtr.h"
@@ -389,6 +390,11 @@ nsNodeInfoManager::SetDocumentPrincipal(nsIPrincipal *aPrincipal)
   }
 
   NS_ASSERTION(aPrincipal, "Must have principal by this point!");
+  MOZ_DIAGNOSTIC_ASSERT(!nsContentUtils::IsExpandedPrincipal(aPrincipal),
+                        "Documents shouldn't have an expanded principal");
+  if (nsContentUtils::IsExpandedPrincipal(aPrincipal)) {
+    Telemetry::Accumulate(Telemetry::DOCUMENT_WITH_EXPANDED_PRINCIPAL, 1);
+  }
 
   mPrincipal = aPrincipal;
 }

toolkit/components/telemetry/Histograms.json

@@ -10490,5 +10490,12 @@
     "kind": "enumerated",
     "n_values": 4,
     "description": "Counts the number of asm.js vs WebAssembly modules instanciations, at the time modules are getting instanciated."
+  },
+  "DOCUMENT_WITH_EXPANDED_PRINCIPAL": {
+    "alert_emails": ["dev-platform@lists.mozilla.org"],
+    "bug_numbers": [1301123],
+    "expires_in_version": "58",
+    "kind": "count",
+    "description": "Number of documents encountered using an expanded principal."
   }
 }