[tracing] Track number of allocations in heap profiler

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 8544c78eb2cd34c3f7693fa4063ccdcf85f837a1..98d835181d014fa57a29e2b193fcd9457c17b026 100644
--- a/base/trace_event/heap_profiler_allocation_context.h
+++ b/base/trace_event/heap_profiler_allocation_context.h
@@ -45,6 +45,12 @@ struct BASE_EXPORT Backtrace {
   StackFrame frames[12];
 };
 
+// Struct to store the size and count of the allocations.
+struct AllocationMetrics {
+  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