base: Introduce SharedMemoryTracker for POSIX (but not macOS)

base/memory/shared_memory_tracker.h

Index: base/memory/shared_memory_tracker.h
diff --git a/base/memory/shared_memory_tracker.h b/base/memory/shared_memory_tracker.h
new file mode 100644
index 0000000000000000000000000000000000000000..fe1a3dd392177b0c20bb5b2daf6498d85eae7e0b
--- /dev/null
+++ b/base/memory/shared_memory_tracker.h
@@ -0,0 +1,56 @@
+// 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.
+
+#ifndef BASE_MEMORY_SHARED_MEMORY_TRACKER_H_
+#define BASE_MEMORY_SHARED_MEMORY_TRACKER_H_
+
+#include "base/memory/shared_memory.h"
+#include "base/synchronization/lock.h"
+#include "base/trace_event/memory_dump_provider.h"
+
+namespace base {
+
+namespace trace_event {
+class ProcessMemoryDump;
+}
+
+// SharedMemoryTracker tracks shared memory usage.
+class BASE_EXPORT SharedMemoryTracker
+    : public base::trace_event::MemoryDumpProvider {
+ public:
+  // Returns a singleton instance.
+  static SharedMemoryTracker* GetInstance();
+
+  // Records shared memory usage on mapping.
+  void IncrementMemoryUsage(const SharedMemory& shared_memory);
+
+  // Records shared memory usage on unmapping.
+  void DecrementMemoryUsage(const SharedMemory& shared_memory);
+
+ private:
+  struct Usage {
+    Usage();
+    Usage(const Usage& rhs);
+    ~Usage();
+    SharedMemory::UniqueId unique_id;
+    size_t size;
+  };
+
+  SharedMemoryTracker();
+  ~SharedMemoryTracker() override;
+
+  // base::trace_event::MemoryDumpProvider implementation.
+  bool OnMemoryDump(const base::trace_event::MemoryDumpArgs& args,
+                    base::trace_event::ProcessMemoryDump* pmd) override;
+
+  // Used to lock when |usages_| is modified or read.
+  Lock usages_lock_;
+  std::unordered_map<const SharedMemory*, Usage> usages_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedMemoryTracker);
+};
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_SHARED_MEMORY_TRACKER_H_