Revert of mac: Remove POSIX shared memory.

mojo/edk/embedder/platform_shared_buffer.cc

Index: mojo/edk/embedder/platform_shared_buffer.cc
diff --git a/mojo/edk/embedder/platform_shared_buffer.cc b/mojo/edk/embedder/platform_shared_buffer.cc
index 63c0a5e6c15b725eb4cbc107a71d0365128a6769..a29a7abd76152ee45f35f6f91d02a1ce2f33c159 100644
--- a/mojo/edk/embedder/platform_shared_buffer.cc
+++ b/mojo/edk/embedder/platform_shared_buffer.cc
@@ -27,7 +27,14 @@
 #elif defined(OS_WIN)
   return ScopedPlatformHandle(PlatformHandle(memory_handle.GetHandle()));
 #else
-  return ScopedPlatformHandle(PlatformHandle(memory_handle.GetMemoryObject()));
+  if (memory_handle.GetType() == base::SharedMemoryHandle::MACH) {
+    return ScopedPlatformHandle(PlatformHandle(
+        memory_handle.GetMemoryObject()));
+  } else {
+    DCHECK(memory_handle.GetType() == base::SharedMemoryHandle::POSIX);
+    return ScopedPlatformHandle(PlatformHandle(
+        memory_handle.GetFileDescriptor().fd));
+  }
 #endif
 }
 
@@ -189,6 +196,9 @@
   options.size = num_bytes_;
   // By default, we can share as read-only.
   options.share_read_only = true;
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  options.type = base::SharedMemoryHandle::MACH;
+#endif
 
   shared_memory_.reset(new base::SharedMemory);
   return shared_memory_->Create(options);
@@ -203,8 +213,12 @@
                                   base::GetCurrentProcId());
 #elif defined(OS_MACOSX) && !defined(OS_IOS)
   base::SharedMemoryHandle handle;
-  handle = base::SharedMemoryHandle(platform_handle.release().port, num_bytes_,
-                                    base::GetCurrentProcId());
+  if (platform_handle.get().type == PlatformHandle::Type::MACH) {
+    handle = base::SharedMemoryHandle(
+        platform_handle.release().port, num_bytes_, base::GetCurrentProcId());
+  } else {
+    handle = base::SharedMemoryHandle(platform_handle.release().handle, false);
+  }
 #else
   base::SharedMemoryHandle handle(platform_handle.release().handle, false);
 #endif