Update from https://crrev.com/308331

base/memory/shared_memory_posix.cc

 // Copyright (c) 2012 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.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
@@ skipping 62 matching lines @@
       mapped_size_(0),
       memory_(NULL),
       read_only_(read_only),
       requested_size_(0) {
   // We don't handle this case yet (note the ignored parameter); let's die if
   // someone comes calling.
   NOTREACHED();
 }
 
 SharedMemory::~SharedMemory() {
+  Unmap();
   Close();
 }
 
 // static
 bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
   return handle.fd >= 0;
 }
 
 // static
 SharedMemoryHandle SharedMemory::NULLHandle() {
@@ skipping 231 matching lines @@
   memory_ = NULL;
   mapped_size_ = 0;
   return true;
 }
 
 SharedMemoryHandle SharedMemory::handle() const {
   return FileDescriptor(mapped_file_, false);
 }
 
 void SharedMemory::Close() {
-  Unmap();
-
   if (mapped_file_ > 0) {
     if (close(mapped_file_) < 0)
       PLOG(ERROR) << "close";
     mapped_file_ = -1;
   }
   if (readonly_mapped_file_ > 0) {
     if (close(readonly_mapped_file_) < 0)
       PLOG(ERROR) << "close";
     readonly_mapped_file_ = -1;
   }
@@ skipping 115 matching lines @@
 
   const int new_fd = dup(handle_to_dup);
   if (new_fd < 0) {
     DPLOG(ERROR) << "dup() failed.";
     return false;
   }
 
   new_handle->fd = new_fd;
   new_handle->auto_close = true;
 
-  if (close_self)
+  if (close_self) {
+    Unmap();
     Close();
+  }
 
   return true;
 }
 
 }  // namespace base