Bug 1209933 - Make sure all parent runtime pointers are the topmost parent, r=billm.

js/src/jsapi.cpp

@@ -668,11 +668,9 @@ JS_NewRuntime(uint32_t maxbytes, uint32_t maxNurseryBytes, JSRuntime* parentRunt
     MOZ_ASSERT(jsInitState == Running,
                "must call JS_Init prior to creating any JSRuntimes");
 
-    // Any parent runtime should be the topmost parent. This assert
-    // isn't required for correctness, but ensuring that the parent
-    // runtime is not destroyed before this one is more easily done
-    // for the main runtime in the process.
-    MOZ_ASSERT_IF(parentRuntime, !parentRuntime->parentRuntime);
+    // Make sure that all parent runtimes are the topmost parent.
+    while (parentRuntime && parentRuntime->parentRuntime)
+        parentRuntime = parentRuntime->parentRuntime;
 
     JSRuntime* rt = js_new<JSRuntime>(parentRuntime);
     if (!rt)