Update from https://crrev.com/327068

base/trace_event/process_memory_dump.h

 // Copyright 2015 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_TRACE_EVENT_PROCESS_MEMORY_DUMP_H_
 #define BASE_TRACE_EVENT_PROCESS_MEMORY_DUMP_H_
 
 #include "base/base_export.h"
 #include "base/containers/hash_tables.h"
 #include "base/containers/small_map.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_vector.h"
 #include "base/trace_event/memory_allocator_dump.h"
+#include "base/trace_event/memory_dump_session_state.h"
 #include "base/trace_event/process_memory_maps.h"
 #include "base/trace_event/process_memory_totals.h"
 
 namespace base {
 namespace trace_event {
 
 class ConvertableToTraceFormat;
 class MemoryDumpManager;
+class MemoryDumpSessionState;
 
 // ProcessMemoryDump is as a strongly typed container which enforces the data
-// model for each memory dump point and holds the dumps produced by the
+// model for each memory dump and holds the dumps produced by the
 // MemoryDumpProvider(s) for a specific process.
 // At trace generation time (i.e. when AsValue() is called), ProcessMemoryDump
 // will compose a key-value dictionary of the various dumps obtained at trace
 // dump point time.
 class BASE_EXPORT ProcessMemoryDump {
  public:
+  // Maps allocator dumps absolute names (allocator_name/heap/subheap) to
+  // MemoryAllocatorDump instances.
   using AllocatorDumpsMap =
       SmallMap<hash_map<std::string, MemoryAllocatorDump*>>;
 
-  ProcessMemoryDump();
+  ProcessMemoryDump(const scoped_refptr<MemoryDumpSessionState>& session_state);
   ~ProcessMemoryDump();
 
   // Called at trace generation time to populate the TracedValue.
   void AsValueInto(TracedValue* value) const;
 
   ProcessMemoryTotals* process_totals() { return &process_totals_; }
   bool has_process_totals() const { return has_process_totals_; }
   void set_has_process_totals() { has_process_totals_ = true; }
 
   ProcessMemoryMaps* process_mmaps() { return &process_mmaps_; }
   bool has_process_mmaps() const { return has_process_mmaps_; }
   void set_has_process_mmaps() { has_process_mmaps_ = true; }
 
   // Creates a new MemoryAllocatorDump with the given name and returns the
-  // empty object back to the caller. The |name| must be unique in the dump.
-  // ProcessMemoryDump handles the memory ownership of the created object.
-  // |parent| can be used to specify a hierarchical relationship of the
-  // allocator dumps.
-  MemoryAllocatorDump* CreateAllocatorDump(const std::string& name);
-  MemoryAllocatorDump* CreateAllocatorDump(const std::string& name,
-                                           MemoryAllocatorDump* parent);
+  // empty object back to the caller.
+  // Arguments:
+  //   allocator_name: a name that univocally identifies allocator dumps
+  //     produced by this provider. It acts as a type w.r.t. the allocator
+  //     attributes, in the sense that all the MAD with the same allocator_name
+  //     are expected to have the same attributes.
+  //   heap_name, either:
+  //     - kRootHeap: if the allocator has only one default heap.
+  //     - a string identifing a heap name (e.g., isolate1, isolate2 ...). It is
+  //       possible to specify nesting by using a path-like string (e.g.,
+  //       isolate1/heap_spaceX, isolate1/heap_spaceY, isolate2/heap_spaceX).
+  // The tuple (|allocator_name|, |heap_name|) is unique inside a PMD.
+  // ProcessMemoryDump handles the memory ownership of its MemoryAllocatorDumps.
+  MemoryAllocatorDump* CreateAllocatorDump(const std::string& allocator_name,
+                                           const std::string& heap_name);
 
-  // Returns a MemoryAllocatorDump given its name or nullptr if not found.
-  MemoryAllocatorDump* GetAllocatorDump(const std::string& name) const;
+  // Looks up a MemoryAllocatorDump given its allocator and heap names, or
+  // nullptr if not found.
+  MemoryAllocatorDump* GetAllocatorDump(const std::string& allocator_name,
+                                        const std::string& heap_name) const;
 
   // Returns the map of the MemoryAllocatorDumps added to this dump.
   const AllocatorDumpsMap& allocator_dumps() const { return allocator_dumps_; }
 
+  const scoped_refptr<MemoryDumpSessionState>& session_state() const {
+    return session_state_;
+  }
+
  private:
   ProcessMemoryTotals process_totals_;
   bool has_process_totals_;
 
   ProcessMemoryMaps process_mmaps_;
   bool has_process_mmaps_;
 
-  // A maps of "allocator_name" -> MemoryAllocatorDump populated by
-  // allocator dump providers.
   AllocatorDumpsMap allocator_dumps_;
 
   // ProcessMemoryDump handles the memory ownership of all its belongings.
   ScopedVector<MemoryAllocatorDump> allocator_dumps_storage_;
 
+  // State shared among all PMDs instances created in a given trace session.
+  scoped_refptr<MemoryDumpSessionState> session_state_;
+
   DISALLOW_COPY_AND_ASSIGN(ProcessMemoryDump);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_PROCESS_MEMORY_DUMP_H_