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

base/memory/shared_memory_posix.cc

Index: base/memory/shared_memory_posix.cc
diff --git a/base/memory/shared_memory_posix.cc b/base/memory/shared_memory_posix.cc
index 91fd3529e0f7dae080b558de42bee6de77193740..e3f333d657eb76e70d224251420e0931139747fe 100644
--- a/base/memory/shared_memory_posix.cc
+++ b/base/memory/shared_memory_posix.cc
@@ -359,23 +359,4 @@ SharedMemoryHandle SharedMemory::GetReadOnlyHandle() {
   return readonly_shm_.Duplicate();
 }
 
-bool SharedMemory::GetUniqueId(SharedMemory::UniqueId* id) const {
-  // This function is called just after mmap. fstat is a system call that might
-  // cause I/O. It's safe to call fstat here because mmap for shared memory is
-  // called in two cases:
-  // 1) To handle file-mapped memory
-  // 2) To handle annonymous shared memory
-  // In 1), I/O is already permitted. In 2), the backend is on page cache and
-  // fstat doesn't cause I/O access to the disk. See the discussion at
-  // crbug.com/604726#c41.
-  base::ThreadRestrictions::ScopedAllowIO allow_io;
-  struct stat file_stat;
-  if (HANDLE_EINTR(
-          ::fstat(static_cast<int>(handle().GetHandle()), &file_stat)) != 0)
-    return false;
-  id->first = file_stat.st_dev;
-  id->second = file_stat.st_ino;
-  return true;
-}
-
 }  // namespace base