Declare pool_ as id instead of NSAutoreleasePool.

testing/platform_test.h

 // Copyright (c) 2006-2008 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 TESTING_PLATFORM_TEST_H_
 #define TESTING_PLATFORM_TEST_H_
 
 #include <gtest/gtest.h>
 
 #if defined(GTEST_OS_MAC)
-#ifdef __OBJC__
-@class NSAutoreleasePool;
-#else
-class NSAutoreleasePool;
+#ifndef __OBJC__
+typedef void* id;
 #endif
 
 // The purpose of this class us to provide a hook for platform-specific
 // operations across unit tests.  For example, on the Mac, it creates and
 // releases an outer NSAutoreleasePool for each test case.  For now, it's only
 // implemented on the Mac.  To enable this for another platform, just adjust
 // the #ifdefs and add a platform_test_<platform>.cc implementation file.
 class PlatformTest : public testing::Test {
  public:
   virtual ~PlatformTest();
 
  protected:
   PlatformTest();
 
  private:
-  NSAutoreleasePool* pool_;
+  // |pool_| is a NSAutoreleasePool, but since this header may be imported from
+  // files built with Objective-C ARC that forbids explicit usage of
+  // NSAutoreleasePools, it is declared as id here.
+  id pool_;
 };
 #else
 typedef testing::Test PlatformTest;
 #endif // GTEST_OS_MAC
 
 #endif // TESTING_PLATFORM_TEST_H_