[tracing] Implement composable memory usage estimators.

base/allocator/allocator_shim.h

 // Copyright 2016 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_ALLOCATOR_ALLOCATOR_SHIM_H_
 #define BASE_ALLOCATOR_ALLOCATOR_SHIM_H_
 
 #include <stddef.h>
 
 #include "base/base_export.h"
@@ skipping 26 matching lines @@
 //   ultimately routes the calls to the actual allocator defined by the build
 //   config (tcmalloc, glibc, ...).
 //
 // It is possible to dynamically insert further AllocatorDispatch stages
 // to the front of the chain, for debugging / profiling purposes.
 //
 // All the functions must be thred safe. The shim does not enforce any
 // serialization. This is to route to thread-aware allocators (e.g, tcmalloc)
 // wihout introducing unnecessary perf hits.
 
-struct AllocatorDispatch {
+struct BASE_EXPORT AllocatorDispatch {
   using AllocFn = void*(const AllocatorDispatch* self, size_t size);
   using AllocZeroInitializedFn = void*(const AllocatorDispatch* self,
                                        size_t n,
                                        size_t size);
   using AllocAlignedFn = void*(const AllocatorDispatch* self,
                                size_t alignment,
                                size_t size);
   using ReallocFn = void*(const AllocatorDispatch* self,
                           void* address,
                           size_t size);
@@ skipping 36 matching lines @@
 
 // Test-only. Rationale: (1) lack of use cases; (2) dealing safely with a
 // removal of arbitrary elements from a singly linked list would require a lock
 // in malloc(), which we really don't want.
 BASE_EXPORT void RemoveAllocatorDispatchForTesting(AllocatorDispatch* dispatch);
 
 }  // namespace allocator
 }  // namespace base
 
 #endif  // BASE_ALLOCATOR_ALLOCATOR_SHIM_H_