Bug 1345961 - Fixing an assertion about OriginAttribute comparison in PostMessage, r=tjr

The OriginAttributes of the 2 windows must match but ignoring the
FirstPartDomain isolation.

dom/base/PostMessageEvent.cpp

@@ -106,18 +106,17 @@ PostMessageEvent::Run()
     //       now.  Long-term, we want HTML5 to address this so that we can
     //       be compliant while being safer.
     if (!targetPrin->Equals(mProvidedPrincipal)) {
+      MOZ_DIAGNOSTIC_ASSERT(ChromeUtils::IsOriginAttributesEqualIgnoringFPD(mProvidedPrincipal->OriginAttributesRef(),
+                                                                            targetPrin->OriginAttributesRef()),
+                            "Unexpected postMessage call to a window with mismatched "
+                            "origin attributes");
+
       nsAutoString providedOrigin, targetOrigin;
       nsresult rv = nsContentUtils::GetUTFOrigin(targetPrin, targetOrigin);
       NS_ENSURE_SUCCESS(rv, rv);
       rv = nsContentUtils::GetUTFOrigin(mProvidedPrincipal, providedOrigin);
       NS_ENSURE_SUCCESS(rv, rv);
 
-      MOZ_DIAGNOSTIC_ASSERT(providedOrigin != targetOrigin ||
-                            (mProvidedPrincipal->OriginAttributesRef() ==
-                              targetPrin->OriginAttributesRef()),
-                            "Unexpected postMessage call to a window with mismatched "
-                            "origin attributes");
-
       const char16_t* params[] = { providedOrigin.get(), targetOrigin.get() };
 
       nsContentUtils::ReportToConsole(nsIScriptError::errorFlag,