[tracing] Track number of allocations in heap profiler

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 <stddef.h>
 #include <stdint.h>
 
@@ skipping 27 matching lines @@
 using StackFrame = const char*;
 
 struct BASE_EXPORT Backtrace {
   // Unused backtrace frames are filled with nullptr frames. If the stack is
   // higher than what can be stored here, the bottom frames are stored. Based
   // on the data above, a depth of 12 captures the full stack in the vast
   // majority of the cases.
   StackFrame frames[12];
 };
 
+// Struct to store the size and count of the allocations.
+struct AllocationsSizeAndCount {

[Dmitry Skiba, 2016/04/14 19:07:30]

You call this 'metrics' everywhere else (metrics_by_context), so lets call it
AllocationMetrics?

[Primiano Tucci (use gerrit), 2016/04/14 19:37:21]

+1

[ssid, 2016/04/14 20:17:10]

Done.

+  size_t size;
+  size_t count;
+};
+
 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:
   // An allocation context with empty backtrace and unknown type.
   static AllocationContext Empty();
@@ skipping 30 matching lines @@
 };
 
 template <>
 struct BASE_EXPORT 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_