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

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..e867f8b7fd5b624b99eefe268f6506490d5227a7
--- /dev/null
+++ b/base/memory/shared_memory_tracker.h
@@ -0,0 +1,66 @@
+// 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/atomicops.h"
+#include "base/memory/shared_memory_handle.h"
+#include "base/memory/singleton.h"
+#include "base/trace_event/memory_dump_provider.h"
+
+namespace base {
+
+class SharedMemory;
+
+namespace trace_event {
+
+class MemoryAllocatorDumpGuid;
+class ProcessMemoryDump;
+}
+
+class BASE_EXPORT SharedMemoryTracker
+    : public base::trace_event::MemoryDumpProvider {
+ public:
+  // Returns a singleton instance.
+  static SharedMemoryTracker* GetInstance();
+
+  static bool AddOwnershipEdgeToSharedGlobalDump(
+      trace_event::ProcessMemoryDump* pmd,
+      const trace_event::MemoryAllocatorDumpGuid& source,
+      const base::SharedMemoryHandle& shared_memory_handle,
+      size_t mapped_size);
+
+  // base::trace_event::MemoryDumpProvider implementation.
+  bool OnMemoryDump(const base::trace_event::MemoryDumpArgs& args,
+                    base::trace_event::ProcessMemoryDump* pmd) override;
+
+  bool IncrementMemoryUsage(const SharedMemory& shared_memory);
+  bool DecrementMemoryUsage(const SharedMemory& shared_memory);
+
+ private:
+  struct TrackerBucket {
+    TrackerBucket();
+    ~TrackerBucket();
+    base::Lock lock;
+    // The first map's key is a device ID and the second map's key is a file
+    // ID. See SharedMemoryHandleID struct.
+    std::unordered_map<int64_t, std::unordered_map<int64_t, size_t>> usage;

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

I don't think you should expose device id and file id here. I think there is a
cleaner option:
add hash operators to SharedMemoryHandleID  and make this
unordered_map<SharedMemoryHandleId, size_t>

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

Done.

+  };
+
+  friend struct base::DefaultSingletonTraits<SharedMemoryTracker>;
+
+  static const int kTrackerBucketNum = 1024;
+
+  SharedMemoryTracker();
+  ~SharedMemoryTracker() override;
+
+  TrackerBucket buckets_[kTrackerBucketNum];
+
+  DISALLOW_COPY_AND_ASSIGN(SharedMemoryTracker);
+};
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_SHARED_MEMORY_TRACKER_H_