[tracing] Add support to pre-load and merge ProcessMemoryDump(s).

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"
@@ skipping 23 matching lines @@
   // MemoryAllocatorDump instances.
   using AllocatorDumpsMap =
       SmallMap<hash_map<std::string, MemoryAllocatorDump*>>;
 
   ProcessMemoryDump(const scoped_refptr<MemoryDumpSessionState>& session_state);
   ~ProcessMemoryDump();
 
   // Called at trace generation time to populate the TracedValue.
   void AsValueInto(TracedValue* value) const;
 
+  // Merges all MemoryAllocatorDump(s) contained in |other| inside this
+  // ProcessMemoryDump, transferring their ownership to this instance.
+  // |other| will be an empty ProcessMemoryDump after this method returns.
+  // This is to allow dump providers to pre-populate ProcessMemoryDump instances
+  // and later move their contents into the ProcessMemoryDump passed as argument
+  // of the MemoryDumpProvider::OnMemoryDump(ProcessMemoryDump*) callback.
+  void TakeAllDumpsFrom(ProcessMemoryDump* other);
+
   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.
@@ skipping 31 matching lines @@
   // 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_