base: Introduce SharedMemoryTracker for POSIX (but not macOS)

base/memory/shared_memory.h

 // 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.
 
 #ifndef BASE_MEMORY_SHARED_MEMORY_H_
 #define BASE_MEMORY_SHARED_MEMORY_H_
 
 #include <stddef.h>
 
 #include <string>
@@ skipping 237 matching lines @@
   //   bool ok = ShareToProcess(process, new_handle);
   //   Close();
   //   return ok;
   // Note that the memory is unmapped by calling this method, regardless of the
   // return value.
   bool GiveToProcess(ProcessHandle process,
                      SharedMemoryHandle* new_handle) {
     return ShareToProcessCommon(process, new_handle, true, SHARE_CURRENT_MODE);
   }
 
+#if defined(OS_POSIX) && !(defined(OS_MACOSX) && !defined(OS_IOS)) && \

[danakj, 2017/01/27 16:56:42]

POSIX && (!MACOSX || IOS) && !NACL avoids double negation.

[hajimehoshi, 2017/02/07 12:33:44]

Done.

+    !defined(OS_NACL)
+  using Id = std::pair<dev_t, ino_t>;

[danakj, 2017/01/27 16:56:42]

I think the type alias just makes use of first/second unclear in the tracker.
I'd prefer to use the pair type literally.

[hajimehoshi, 2017/02/07 12:33:44]

This can be different type among Windows, macOS and other POSIX, so I want to
keep this type alias.

+
+  bool GetUniqueId(Id* id) const;

[danakj, 2017/01/27 16:56:42]

Can you make a comment that this goes to the file system ie can block and is
slow.

[hajimehoshi, 2017/02/07 12:33:44]

Done.

+#endif
+
  private:
 #if defined(OS_POSIX) && !defined(OS_NACL) && !defined(OS_ANDROID) && \
     !(defined(OS_MACOSX) && !defined(OS_IOS))
   bool FilePathForMemoryName(const std::string& mem_name, FilePath* path);
 #endif
 
   enum ShareMode {
     SHARE_READONLY,
     SHARE_CURRENT_MODE,
   };
@@ skipping 26 matching lines @@
   int                mapped_file_;
   int                readonly_mapped_file_;
 #endif
   size_t             mapped_size_;
   void*              memory_;
   bool               read_only_;
   size_t             requested_size_;
 
   DISALLOW_COPY_AND_ASSIGN(SharedMemory);
 };
+
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_H_