[Tracing] Make heap profiler type info a string

base/trace_event/heap_profiler_allocation_context.h

Index: base/trace_event/heap_profiler_allocation_context.h
diff --git a/base/trace_event/heap_profiler_allocation_context.h b/base/trace_event/heap_profiler_allocation_context.h
index c5f1fdfa750e18686b18a387a6cfd4c63a9552a9..68921634560c2ed48fbb113fd07522f38012ab60 100644
--- a/base/trace_event/heap_profiler_allocation_context.h
+++ b/base/trace_event/heap_profiler_allocation_context.h
@@ -52,17 +52,17 @@ bool BASE_EXPORT operator==(const Backtrace& lhs, const Backtrace& rhs);
 // 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;