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

base/memory/shared_memory_tracker.h

 // 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 <unordered_map>
 
 #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 MemoryAllocatorDumpGuid;
 class ProcessMemoryDump;
 }
 
 // SharedMemoryTracker tracks shared memory usage.
 class BASE_EXPORT SharedMemoryTracker
     : public base::trace_event::MemoryDumpProvider {
  public:
   // Returns a singleton instance.
   static SharedMemoryTracker* GetInstance();
 
+  // Adds two ownership edges between the given guid |source| and its global
+  // shared memory dump. This helps to get accurate effective size of modules
+  // that backend is shared memory.
+  static bool AddOwnershipEdges(
+      trace_event::ProcessMemoryDump* pmd,
+      const trace_event::MemoryAllocatorDumpGuid& source,
+      const SharedMemory& shared_memory);
+
   // 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;
+  bool OnMemoryDump(const trace_event::MemoryDumpArgs& args,
+                    trace_event::ProcessMemoryDump* pmd) override;
 
   // Used to lock when |usages_| is modified or read.
   Lock usages_lock_;
-  std::unordered_map<const SharedMemory*, Usage> usages_;
+  std::unordered_map<const SharedMemory*, size_t> usages_;
 
   DISALLOW_COPY_AND_ASSIGN(SharedMemoryTracker);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_TRACKER_H_