[mojo-edk] Switch shared buffers to use Mach on OSX.

mojo/edk/system/shared_buffer_unittest.cc

 // Copyright 2015 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 <string.h>
 
 #include <string>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 198 matching lines @@
     std::string message = ReadMessageWithHandles(parent, &pipe, 1);
     WriteMessageWithHandles(child, message, &pipe, 1);
 
     EXPECT_EQ("quit", ReadMessage(parent));
     WriteMessage(child, "quit");
     EXPECT_EQ("ok", ReadMessage(child));
     WriteMessage(parent, "ok");
   END_CHILD()
 }
 
-#if defined(OS_ANDROID)
+#if defined(OS_ANDROID) || defined(OS_MACOSX)
 // Android multi-process tests are not executing the new process. This is flaky.
+// Passing shared memory handles between cousins is not currently supported on
+// OSX.
 #define MAYBE_PassHandleBetweenCousins DISABLED_PassHandleBetweenCousins
 #else
 #define MAYBE_PassHandleBetweenCousins PassHandleBetweenCousins
 #endif
 TEST_F(SharedBufferTest, MAYBE_PassHandleBetweenCousins) {
   const std::string message = "hello";
   MojoHandle p0, p1;
   CreateMessagePipe(&p0, &p1);
 
   // Spawn two children who will each spawn their own child. Make sure the
@@ skipping 19 matching lines @@
 
   // The second grandchild should have written this message.
   ExpectBufferContents(b, 0, message);
 }
 
 #endif  // !defined(OS_IOS)
 
 }  // namespace
 }  // namespace edk
 }  // namespace mojo