Resurrect POSIX shared memory support on mac

components/nacl/loader/nacl_ipc_adapter.cc

Index: components/nacl/loader/nacl_ipc_adapter.cc
diff --git a/components/nacl/loader/nacl_ipc_adapter.cc b/components/nacl/loader/nacl_ipc_adapter.cc
index 3b1110251d1905d6fa2b9aa914dda0a3921d380c..db6bb56f1e39a90c149f21f2613d70a9ddd20f61 100644
--- a/components/nacl/loader/nacl_ipc_adapter.cc
+++ b/components/nacl/loader/nacl_ipc_adapter.cc
@@ -234,8 +234,13 @@ std::unique_ptr<NaClDescWrapper> MakeShmNaClDesc(
     const base::SharedMemoryHandle& handle,
     size_t size) {
 #if defined(OS_MACOSX)
-  return std::unique_ptr<NaClDescWrapper>(new NaClDescWrapper(
-      NaClDescImcShmMachMake(handle.GetMemoryObject(), size)));
+  if (handle.GetType() == base::SharedMemoryHandle::MACH) {
+    return std::unique_ptr<NaClDescWrapper>(new NaClDescWrapper(
+        NaClDescImcShmMachMake(handle.GetMemoryObject(), size)));
+  } else {
+    CHECK_EQ(base::SharedMemoryHandle::POSIX, handle.GetType());
+    return nullptr;
+  }
 #else
   return std::unique_ptr<NaClDescWrapper>(
       new NaClDescWrapper(NaClDescImcShmMake(