[tracing] Introduce support for userland memory allocators dumps.

base/trace_event/memory_dump_manager.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_MEMORY_DUMP_MANAGER_H_
 #define BASE_TRACE_EVENT_MEMORY_DUMP_MANAGER_H_
 
 #include <vector>
 
 #include "base/atomicops.h"
@@ skipping 31 matching lines @@
   void UnregisterDumpProvider(MemoryDumpProvider* mdp);
 
   // Requests a memory dump. The dump might happen or not depending on the
   // filters and categories specified when enabling tracing.
   void RequestDumpPoint(DumpPointType dump_point_type);
 
   // TraceLog::EnabledStateObserver implementation.
   void OnTraceLogEnabled() override;
   void OnTraceLogDisabled() override;
 
+  // Returns the MemoryDumpProvider which is currently being dumping into a
+  // ProcessMemoryDump via DumpInto(...) if any, nullptr otherwise.
+  MemoryDumpProvider* dump_provider_currently_active() const {
+    return dump_provider_currently_active_;
+  }
+
  private:
   friend struct DefaultDeleter<MemoryDumpManager>;  // For the testing instance.
   friend struct DefaultSingletonTraits<MemoryDumpManager>;
   friend class MemoryDumpManagerTest;
 
   static const char kTraceCategory[];
 
   static void SetInstanceForTesting(MemoryDumpManager* instance);
 
   MemoryDumpManager();
   virtual ~MemoryDumpManager();
 
   // Broadcasts the dump requests to the other processes.
   void BroadcastDumpRequest();
 
   // Creates a dump point for the current process and appends it to the trace.
   void CreateLocalDumpPoint(DumpPointType dump_point_type, uint64 guid);
 
   std::vector<MemoryDumpProvider*> dump_providers_registered_;  // Not owned.
   std::vector<MemoryDumpProvider*> dump_providers_enabled_;     // Not owned.
+  MemoryDumpProvider* dump_provider_currently_active_;          // Now owned.
 
   // Protects from concurrent accesses to the |dump_providers_*|, e.g., tearing
   // down logging while creating a dump point on another thread.
   Lock lock_;
 
   // Optimization to avoid attempting any dump point (i.e. to not walk an empty
   // dump_providers_enabled_ list) when tracing is not enabled.
   subtle::AtomicWord memory_tracing_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(MemoryDumpManager);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_MEMORY_DUMP_MANAGER_H_