[tracing] Simplify design of MemoryAllocatorDump

base/trace_event/memory_dump_manager.cc

Index: base/trace_event/memory_dump_manager.cc
diff --git a/base/trace_event/memory_dump_manager.cc b/base/trace_event/memory_dump_manager.cc
index c593b804a455976cd7bffd8f340a5058cc91bf68..31fe92e2f3163e2faa9c0457176006af2157bee6 100644
--- a/base/trace_event/memory_dump_manager.cc
+++ b/base/trace_event/memory_dump_manager.cc
@@ -311,7 +311,13 @@ void MemoryDumpManager::OnTraceLogEnabled() {
   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);