Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

extensions/renderer/extension_frame_helper.cc

 // Copyright 2013 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.
 
 #include "extensions/renderer/extension_frame_helper.h"
 
 #include "base/strings/string_util.h"
 #include "content/public/renderer/render_frame.h"
 #include "extensions/common/api/messaging/message.h"
 #include "extensions/common/constants.h"
@@ skipping 264 matching lines @@
     const std::string& extension_id,
     const std::string& module_name,
     const std::string& function_name,
     const base::ListValue& args,
     bool user_gesture) {
   extension_dispatcher_->InvokeModuleSystemMethod(render_frame(), extension_id,
                                                   module_name, function_name,
                                                   args, user_gesture);
 }
 
+void ExtensionFrameHelper::OnDestruct() {
+  delete this;
+}
+
 }  // namespace extensions