Issue #618 - Clear the module map when changing a Document's global and add

release build assertions for mismatching compartments.

dom/script/ScriptLoader.h

@@ -506,6 +506,12 @@ public:
     return mPendingChildLoaders.AppendElement(aChild) != nullptr;
   }
 
+  /*
+   * Clear the map of loaded modules. Called when a Document object is reused
+   * for a different global.
+   */
+  void ClearModuleMap();
+
 private:
   virtual ~ScriptLoader();