base: Introduce SharedMemoryTracker for POSIX (but not macOS)

base/memory/shared_memory_handle_posix.cc

Index: base/memory/shared_memory_handle_posix.cc
diff --git a/base/memory/shared_memory_handle_posix.cc b/base/memory/shared_memory_handle_posix.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e4e32107db3ef3ec2310a18ea8de6d08a4a483f2
--- /dev/null
+++ b/base/memory/shared_memory_handle_posix.cc
@@ -0,0 +1,33 @@
+// Copyright 2017 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_handle.h"
+
+#include <sys/stat.h>
+
+#include "base/strings/stringprintf.h"
+
+namespace base {
+
+#if !(defined(OS_MACOSX) && !defined(OS_IOS))
+
+bool GetIDFromSharedMemoryHandle(const SharedMemoryHandle& handle,
+                                 SharedMemoryHandleID* id) {
+  // Get file name?
+  struct stat file_stat;
+  if (fstat(static_cast<int>(handle.fd), &file_stat) != 0)
+    return false;
+  id->device_id = file_stat.st_dev;
+  id->file_id = file_stat.st_ino;
+  return true;
+}
+
+std::string GetSharedMemoryHandleIDString(const SharedMemoryHandleID& id) {
+  return base::StringPrintf("%lld.%lld", static_cast<long long>(id.device_id),
+                            static_cast<long long>(id.file_id));
+}
+
+#endif
+
+}  // namespace base