[tracing] Simplify design of MemoryAllocatorDump

base/trace_event/memory_dump_manager.cc

 // 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.
 
 #include "base/trace_event/memory_dump_manager.h"
 
 #include <algorithm>
 
 #include "base/atomic_sequence_num.h"
 #include "base/compiler_specific.h"
@@ skipping 293 matching lines @@
 void MemoryDumpManager::OnTraceLogEnabled() {
   // TODO(primiano): at this point we query  TraceLog::GetCurrentCategoryFilter
   // to figure out (and cache) which dumpers should be enabled or not.
   // For the moment piggy back everything on the generic "memory" category.
   bool enabled;
   TRACE_EVENT_CATEGORY_GROUP_ENABLED(kTraceCategory, &enabled);
 
   AutoLock lock(lock_);
   dump_providers_enabled_.clear();
   if (enabled) {
+    // Merge the dictionary of allocator attributes from all dump providers
+    // into the session state.
     session_state_ = new MemoryDumpSessionState();
+    for (const MemoryDumpProvider* mdp : dump_providers_registered_) {
+      session_state_->allocators_attributes_type_info.Update(
+          mdp->allocator_attributes_type_info());
+    }
     dump_providers_enabled_ = dump_providers_registered_;
   }
   subtle::NoBarrier_Store(&memory_tracing_enabled_, 1);
 }
 
 void MemoryDumpManager::OnTraceLogDisabled() {
   AutoLock lock(lock_);
   dump_providers_enabled_.clear();
   subtle::NoBarrier_Store(&memory_tracing_enabled_, 0);
   session_state_ = nullptr;
 }
 
 }  // namespace trace_event
 }  // namespace base