[WIP] Add SharedMemoryTracker to dump base::SharedMemory usage

base/memory/shared_memory_handle.h

 // 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.
 
 #ifndef BASE_MEMORY_SHARED_MEMORY_HANDLE_H_
 #define BASE_MEMORY_SHARED_MEMORY_HANDLE_H_
 
 #include <stddef.h>
 
 #include "build/build_config.h"
@@ skipping 168 matching lines @@
       // Whether passing this object as a parameter to an IPC message passes
       // ownership of |memory_object_| to the IPC stack. This is meant to mimic
       // the behavior of the |auto_close| parameter of FileDescriptor.
       // Defaults to |false|.
       bool ownership_passes_to_ipc_;
     };
   };
 };
 #endif
 
+#if defined(OS_POSIX) && !(defined(OS_MACOSX) && !defined(OS_IOS))
+struct SharedMemoryHandleID {
+  dev_t device_id;
+  ino_t file_id;
+};
+#elif defined(OS_MACOSX)
+struct SharedMemoryHandleID {
+  // TODO: On macOS, this might be mach_port_t.
+  dev_t device_id;
+  ino_t file_id;
+};
+#elif defined(OS_WIN)
+struct SharedMemoryHandleID {
+  DWORD device_id;   // BY_HANDLE_FILE_INFORMATION.dwVolumeSerialNumber
+  intt64_t file_id;  // BY_HANDLE_FILE_INFORMATION.nFileIndexHigh and Low
+};
+#endif
+
+bool GetIDFromSharedMemoryHandle(const SharedMemoryHandle& handle,

[Primiano Tucci (use gerrit), 2017/01/20 16:34:52]

should this just be a member function of SharedMemoryHandle? something like
SharedMemoryHandleID SharedMemoryHandle::GetUniqueID() ?
and eventually have the SharedMemoryHandleID struct to have a ToString() method.
I think would be cleaner

[hajimehoshi, 2017/01/23 11:59:09]

I like your suggestion, but on POSIX, SharedMemoryHandle is FileDescriptor, and
I hesitated to add your suggested methods to FileDescriptor. Do you think this
is fine?

[Primiano Tucci (use gerrit), 2017/01/24 01:26:40]

Ahh okay I didn't notice. I think it was always some wrapper class. If this is a
FD class, my proposal becomes controversial. So your approach makes more sense.
Or probably you can reverse it and make it a static factory method of
MemoryHandleId, something like:

class MemoryHandleId {
static SharedMemoryHandleID FromSharedMemoryhandle(const SHM&);
...
}

+                                 SharedMemoryHandleID* id);
+
+std::string GetSharedMemoryHandleIDString(const SharedMemoryHandleID& id);
+
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_HANDLE_H_