[Tracing] Make heap profiler type info a string

base/trace_event/heap_profiler_allocation_context.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_HEAP_PROFILER_ALLOCATION_CONTEXT_H_
 #define BASE_TRACE_EVENT_HEAP_PROFILER_ALLOCATION_CONTEXT_H_
 
 #include <stdint.h>
 
 #include "base/base_export.h"
@@ skipping 34 matching lines @@
 };
 
 bool BASE_EXPORT operator==(const Backtrace& lhs, const Backtrace& rhs);
 
 // The |AllocationContext| is context metadata that is kept for every allocation
 // when heap profiling is enabled. To simplify memory management for book-
 // keeping, this struct has a fixed size. All |const char*|s here must have
 // static lifetime.
 struct BASE_EXPORT AllocationContext {
  public:
-  // A type ID is a number that is unique for every C++ type. A type ID is
-  // stored instead of the type name to avoid inflating the binary with type
-  // name strings. There is an out of band lookup table mapping IDs to the type
-  // names. A value of 0 means that the type is not known.
-  using TypeId = uint16_t;
-
-  // An allocation context with empty backtrace and type ID 0 (unknown type).
+  // An allocation context with empty backtrace and unknown type.
   static AllocationContext Empty();
 
   Backtrace backtrace;
-  TypeId type_id;
+
+  // Type name of the type stored in the allocated memory, as returned by

[Primiano Tucci (use gerrit), 2015/11/23 15:46:48]

I'd remove the "as returned by typeid(T)" as it is a bit confusing (w.r.t
production builds that will have manual annotation)

[Ruud van Asseldonk, 2015/11/23 18:23:26]

Done.

+  // |typeid(T).name()|. A null pointer indicates "unknown type". Grouping is
+  // done by comparing pointers, not by deep string comparison. In a component
+  // build, where a type name can have a string literal in several dynamic
+  // libraries, this may distort grouping.
+  const char* type_name;

[Primiano Tucci (use gerrit), 2015/11/23 15:46:47]

in a follow up CL we might just hash this as well and make it work nicely. Not
100% sure in production builds identical strings are deduped by the linker

[Ruud van Asseldonk, 2015/11/23 18:23:26]

We could if it turns out to be an issue, but my experience with
PartitionAlloc/Blink so far is that this is not a problem in practice.

 
  private:
   friend class AllocationContextTracker;
 
   // Don't allow uninitialized instances except inside the allocation context
   // tracker. Except in tests, an |AllocationContext| should only be obtained
   // from the tracker. In tests, paying the overhead of initializing the struct
   // to |Empty| and then overwriting the members is not such a big deal.
   AllocationContext();
 };
@@ skipping 12 matching lines @@
 };
 
 template <>
 struct hash<base::trace_event::AllocationContext> {
   size_t operator()(const base::trace_event::AllocationContext& context) const;
 };
 
 }  // BASE_HASH_NAMESPACE
 
 #endif  // BASE_TRACE_EVENT_HEAP_PROFILER_ALLOCATION_CONTEXT_H_