Add WARN_UNUSED_RESULT to scoped_refptr::release.

chrome/browser/ui/webui/tracing_ui.cc

 // Copyright (c) 2012 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 "chrome/browser/ui/webui/tracing_ui.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 329 matching lines @@
         base::Bind(&ReadTraceFileCallback,
                    make_scoped_refptr(new TaskProxy(AsWeakPtr())), path));
   } else {
     BrowserThread::PostTask(
         BrowserThread::FILE, FROM_HERE,
         base::Bind(&WriteTraceFileCallback,
                    make_scoped_refptr(new TaskProxy(AsWeakPtr())), path,
                    trace_data_to_save_.release()));
   }
 
-  select_trace_file_dialog_.release();
+  select_trace_file_dialog_ = NULL;
 }
 
 void TracingMessageHandler::FileSelectionCanceled(void* params) {
-  select_trace_file_dialog_.release();
+  select_trace_file_dialog_ = NULL;
   if (select_trace_file_dialog_type_ ==
       ui::SelectFileDialog::SELECT_OPEN_FILE) {
     web_ui()->CallJavascriptFunction(
         "tracingController.onLoadTraceFileCanceled");
   } else {
     web_ui()->CallJavascriptFunction(
         "tracingController.onSaveTraceFileCanceled");
   }
 }
 
@@ skipping 177 matching lines @@
 //
 ////////////////////////////////////////////////////////////////////////////////
 
 TracingUI::TracingUI(content::WebUI* web_ui) : WebUIController(web_ui) {
   web_ui->AddMessageHandler(new TracingMessageHandler());
 
   // Set up the chrome://tracing/ source.
   Profile* profile = Profile::FromWebUI(web_ui);
   ChromeURLDataManager::AddDataSource(profile, CreateTracingHTMLSource());
 }