Share field trial allocator on Mac

base/memory/shared_memory_handle_mac.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 "base/memory/shared_memory_handle.h"
 
 #include <mach/mach_vm.h>
 #include <stddef.h>
 #include <sys/mman.h>
 #include <unistd.h>
@@ skipping 49 matching lines @@
     const SharedMemoryHandle& handle) {
   if (this == &handle)
     return *this;
 
   type_ = handle.type_;
   CopyRelevantData(handle);
   return *this;
 }
 
 SharedMemoryHandle SharedMemoryHandle::Duplicate() const {
-  if (!IsValid())
-    return SharedMemoryHandle(MACH_PORT_NULL, 0, 0);
+  switch (type_) {
+    case POSIX: {
+      if (!IsValid())
+        return SharedMemoryHandle();
+      int duped_fd = HANDLE_EINTR(dup(file_descriptor_.fd));
+      if (duped_fd < 0)
+        return SharedMemoryHandle();
+      return SharedMemoryHandle(FileDescriptor(duped_fd, true));
+    }
+    case MACH: {
+      if (!IsValid())
+        return SharedMemoryHandle(MACH_PORT_NULL, 0, 0);
 
-  // Increment the ref count.
-  kern_return_t kr = mach_port_mod_refs(mach_task_self(), memory_object_,
-                                        MACH_PORT_RIGHT_SEND, 1);
-  DCHECK_EQ(kr, KERN_SUCCESS);
-  SharedMemoryHandle handle(*this);
-  handle.SetOwnershipPassesToIPC(true);
-  return handle;
+      // Increment the ref count.
+      kern_return_t kr = mach_port_mod_refs(mach_task_self(), memory_object_,
+                                            MACH_PORT_RIGHT_SEND, 1);
+      DCHECK_EQ(kr, KERN_SUCCESS);
+      SharedMemoryHandle handle(*this);
+      handle.SetOwnershipPassesToIPC(true);
+      return handle;
+    }
+  }
 }
 
 bool SharedMemoryHandle::operator==(const SharedMemoryHandle& handle) const {
   if (!IsValid() && !handle.IsValid())
     return true;
 
   if (type_ != handle.type_)
     return false;
 
   switch (type_) {
@@ skipping 108 matching lines @@
     case MACH:
       memory_object_ = handle.memory_object_;
       size_ = handle.size_;
       pid_ = handle.pid_;
       ownership_passes_to_ipc_ = handle.ownership_passes_to_ipc_;
       break;
   }
 }
 
 }  // namespace base