Declare pool_ as id instead of NSAutoreleasePool.

testing/platform_test.h

Index: testing/platform_test.h
diff --git a/testing/platform_test.h b/testing/platform_test.h
index 04fc845bd99bb1f19421834ee0ca6371eee37ef3..24980fbe0c160a72712b080df243fdf442c77a15 100644
--- a/testing/platform_test.h
+++ b/testing/platform_test.h
@@ -8,10 +8,8 @@
 #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
@@ -27,7 +25,10 @@ class PlatformTest : public testing::Test {
   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;