mac: Back discardable shared memory with a Mach primitive.

base/memory/discardable_shared_memory.cc

 // Copyright 2014 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/discardable_shared_memory.h"
 
 #if defined(OS_POSIX) && !defined(OS_NACL)
 // For madvise() which is available on all POSIX compatible systems.
 #include <sys/mman.h>
 #endif
@@ skipping 104 matching lines @@
 
 DiscardableSharedMemory::~DiscardableSharedMemory() {
 }
 
 bool DiscardableSharedMemory::CreateAndMap(size_t size) {
   CheckedNumeric<size_t> checked_size = size;
   checked_size += AlignToPageSize(sizeof(SharedState));
   if (!checked_size.IsValid())
     return false;
 
-#if defined(OS_MACOSX) && !defined(OS_IOS)
-  // DiscardableSharedMemory does not yet support a Mach-implementation, so
-  // force the underlying primitive to be a POSIX fd. https://crbug.com/547239.
-  if (!shared_memory_.CreateAndMapAnonymousPosix(checked_size.ValueOrDie()))
-    return false;
-#else
   if (!shared_memory_.CreateAndMapAnonymous(checked_size.ValueOrDie()))
     return false;
-#endif  // defined(OS_MACOSX) && !defined(OS_IOS)
 
   mapped_size_ =
       shared_memory_.mapped_size() - AlignToPageSize(sizeof(SharedState));
 
   locked_page_count_ = AlignToPageSize(mapped_size_) / base::GetPageSize();
 #if DCHECK_IS_ON()
   for (size_t page = 0; page < locked_page_count_; ++page)
     locked_pages_.insert(page);
 #endif
 
@@ skipping 270 matching lines @@
 
 void DiscardableSharedMemory::Close() {
   shared_memory_.Close();
 }
 
 Time DiscardableSharedMemory::Now() const {
   return Time::Now();
 }
 
 }  // namespace base