Update from https://crrev.com/311076

base/files/memory_mapped_file_posix.cc

 // Copyright 2013 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/files/memory_mapped_file.h"
 
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
 #include "base/logging.h"
 #include "base/threading/thread_restrictions.h"
 
 namespace base {
 
 MemoryMappedFile::MemoryMappedFile() : data_(NULL), length_(0) {
 }
 
+#if !defined(OS_NACL)
 bool MemoryMappedFile::MapFileRegionToMemory(
     const MemoryMappedFile::Region& region) {
   ThreadRestrictions::AssertIOAllowed();
 
   off_t map_start = 0;
   size_t map_size = 0;
   int32 data_offset = 0;
 
   if (region == MemoryMappedFile::Region::kWholeFile) {
     int64 file_len = file_.GetLength();
@@ skipping 38 matching lines @@
                                    file_.GetPlatformFile(),
                                    map_start));
   if (data_ == MAP_FAILED) {
     DPLOG(ERROR) << "mmap " << file_.GetPlatformFile();
     return false;
   }
 
   data_ += data_offset;
   return true;
 }
+#endif
 
 void MemoryMappedFile::CloseHandles() {
   ThreadRestrictions::AssertIOAllowed();
 
   if (data_ != NULL)
     munmap(data_, length_);
   file_.Close();
 
   data_ = NULL;
   length_ = 0;
 }
 
 }  // namespace base