Extract some logic from transport_dib into shared_memory.

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 187 matching lines @@
     return base::SharedMemory::NULLHandle();
   return base::FileDescriptor(duped_handle, clean_up_resources_on_destruction);
 }
 #endif
 
 bool SharedMemory::CreateAndMapAnonymous(size_t size) {
   return CreateAnonymous(size) && Map(size);
 }
 
 #if !defined(OS_ANDROID)
+// static
+int SharedMemory::GetSizeFromSharedMemoryHandle(
+    const SharedMemoryHandle& handle) {
+  struct stat st;
+  if (fstat(handle.fd, &st) != 0)
+    return st.st_size;
+  return -1;
+}
+
 // Chromium mostly only uses the unique/private shmem as specified by
 // "name == L"". The exception is in the StatsTable.
 // TODO(jrg): there is no way to "clean up" all unused named shmem if
 // we restart from a crash.  (That isn't a new problem, but it is a problem.)
 // In case we want to delete it later, it may be useful to save the value
 // of mem_filename after FilePathForMemoryName().
 bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
   // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466437
   // is fixed.
   tracked_objects::ScopedTracker tracking_profile1(
@@ skipping 330 matching lines @@
 
   if (close_self) {
     Unmap();
     Close();
   }
 
   return true;
 }
 
 }  // namespace base