[Tracing] Make heap profiler type info a string

base/trace_event/heap_profiler_allocation_context_tracker.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/heap_profiler_allocation_context_tracker.h"
 
 #include <algorithm>
 #include <iterator>
 
 #include "base/atomicops.h"
@@ skipping 88 matching lines @@
 
     // Copy as much of the bottom of the pseudo stack into the backtrace as
     // possible.
     for (; src != src_end && dst != dst_end; src++, dst++)
       *dst = *src;
 
     // If there is room for more, fill the remaining slots with empty frames.
     std::fill(dst, dst_end, nullptr);
   }
 
-  ctx.type_id = 0;
+  ctx.type_name = nullptr;
 
   return ctx;
 }
 
 }  // namespace trace_event
 }  // namespace base