Bug 1475262 - Only ignore XUL persist on top level windows. r=smaug

Fixes the incorrect assumption that all XUL <window> elements are top level
windows and will have their attribute persistence handled by the
nsXULWindow. An example of where this assumption fails is the password
manager which opens a <window> within a sub dialog that has no nsXULWindow.

MozReview-Commit-ID: 1f59QPIz42s

--HG--
extra : rebase_source : e91711ead3ba7714d8c6ad241e903dc160ad8bab

dom/xul/XULDocument.cpp

@@ -1092,9 +1092,11 @@ XULDocument::Persist(Element* aElement, int32_t aNameSpaceID,
         return mLocalStore->RemoveValue(uri, id, attrstr);
     }
 
-    // Persisting attributes to windows is handled by nsXULWindow.
+    // Persisting attributes to top level windows is handled by nsXULWindow.
     if (aElement->IsXULElement(nsGkAtoms::window)) {
-        return NS_OK;
+        if (nsCOMPtr<nsIXULWindow> win = GetXULWindowIfToplevelChrome()) {
+           return NS_OK;
+        }
     }
 
     return mLocalStore->SetValue(uri, id, attrstr, valuestr);
@@ -1629,9 +1631,12 @@ XULDocument::ApplyPersistentAttributesToElements(const nsAString &aID,
                  continue;
             }
 
-            // Applying persistent attributes to windows is handled by nsXULWindow.
+            // Applying persistent attributes to top level windows is handled
+            // by nsXULWindow.
             if (element->IsXULElement(nsGkAtoms::window)) {
-                continue;
+                if (nsCOMPtr<nsIXULWindow> win = GetXULWindowIfToplevelChrome()) {
+                    continue;
+                }
             }
 
             Unused << element->SetAttr(kNameSpaceID_None, attr, value, true);