Validation of extension api callback and event parameters in DEBUG

chrome/renderer/extensions/event_bindings.h

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_RENDERER_EXTENSIONS_EVENT_BINDINGS_H_
 #define CHROME_RENDERER_EXTENSIONS_EVENT_BINDINGS_H_
 
 #include <string>
 
 #include "v8/include/v8.h"
@@ skipping 17 matching lines @@
 
   // Handle a script context coming / going away.
   static void HandleContextCreated(WebKit::WebFrame* frame,
                                    bool content_script);
   static void HandleContextDestroyed(WebKit::WebFrame* frame);
 
   // Calls the given function in each registered context which is listening for
   // events.  If render_view is non-NULL, only call the function in contexts
   // belonging to that view.  See comments on
   // bindings_utils::CallFunctionInContext for more details.
+  // The called javascript function should not return a value other than
+  // v8::Undefined(). A DCHECK is setup to break if it is otherwise.
   static void CallFunction(const std::string& function_name, int argc,
                            v8::Handle<v8::Value>* argv,
                            RenderView* render_view);
 };
 
 #endif  // CHROME_RENDERER_EXTENSIONS_EVENT_BINDINGS_H_