Mac: turn on file access checks for the UI thread.

chrome/browser/browser_main.cc

 // Copyright (c) 2010 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/browser_main.h"
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
@@ skipping 465 matching lines @@
   // and 1 if it can't be. This is for validation that the library is installed
   // and versioned properly for Chrome to find.
   if (command_line.HasSwitch(switches::kTestLoadLibcros))
     exit(!chromeos::CrosLibrary::Get()->EnsureLoaded());
 #endif
 }
 
 void RunUIMessageLoop(BrowserProcess* browser_process) {
   TRACE_EVENT_BEGIN("BrowserMain:MESSAGE_LOOP", 0, "");
 
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_MACOSX)
   // If the UI thread blocks, the whole UI is unresponsive.
   // Do not allow disk IO from the UI thread.
   // TODO(evanm): turn this on for all platforms.
   //   http://code.google.com/p/chromium/issues/detail?id=60211
   base::ThreadRestrictions::SetIOAllowed(false);
 #endif
 
 #if defined(TOOLKIT_VIEWS)
   views::AcceleratorHandler accelerator_handler;
   MessageLoopForUI::current()->Run(&accelerator_handler);
@@ skipping 1075 matching lines @@
   metrics->Stop();
 
   // browser_shutdown takes care of deleting browser_process, so we need to
   // release it.
   ignore_result(browser_process.release());
   browser_shutdown::Shutdown();
 
   TRACE_EVENT_END("BrowserMain", 0, 0);
   return result_code;
 }