[tracing] Add native allocation tracing mode.

base/trace_event/heap_profiler_allocation_context.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.h"
 
 #include <cstring>
 
 #include "base/hash.h"
 #include "base/macros.h"
 
 namespace base {
 namespace trace_event {
 
 // Constructor that does not initialize members.
 AllocationContext::AllocationContext() {}
 
 // static
 AllocationContext AllocationContext::Empty() {
   AllocationContext ctx;
 
+  ctx.backtrace.frame_type = STACK_FRAME_TYPE_SYMBOL;
   for (size_t i = 0; i < arraysize(ctx.backtrace.frames); i++)
     ctx.backtrace.frames[i] = nullptr;
 
   ctx.type_name = nullptr;
 
   return ctx;
 }
 
 bool operator==(const Backtrace& lhs, const Backtrace& rhs) {
   // Pointer equality of the stack frames is assumed, so instead of doing a deep
@@ skipping 26 matching lines @@
   // the magic number is coprime to 2^64.
   size_t type_hash = reinterpret_cast<size_t>(ctx.type_name) * 2654435761;
 
   // Multiply one side to break the commutativity of +. Multiplication with a
   // number coprime to |numeric_limits<size_t>::max() + 1| is bijective so
   // randomness is preserved.
   return (backtrace_hash * 3) + type_hash;
 }
 
 }  // BASE_HASH_NAMESPACE