mac: Hook up allocator shim during app startup.

base/allocator/allocator_interception_mac.h

 // Copyright 2017 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_INTERCEPTION_MAC_H_
 #define BASE_ALLOCATOR_ALLOCATOR_INTERCEPTION_MAC_H_
 
 #include <malloc/malloc.h>
 #include <stddef.h>
 
+#include "base/base_export.h"
 #include "third_party/apple_apsl/malloc.h"
 
 namespace base {
 namespace allocator {
 
 typedef void* (*malloc_type)(struct _malloc_zone_t* zone, size_t size);
 typedef void* (*calloc_type)(struct _malloc_zone_t* zone,
                              size_t num_items,
                              size_t size);
 typedef void* (*valloc_type)(struct _malloc_zone_t* zone, size_t size);
@@ skipping 30 matching lines @@
   size_fn_type size = nullptr;
 };
 
 // Saves the function pointers currently used by default zone into |functions|.
 void StoreFunctionsForDefaultZone(MallocZoneFunctions* functions);
 
 // Updates the default malloc zone to use the functions specified by
 // |functions|.
 void ReplaceFunctionsForDefaultZone(const MallocZoneFunctions* functions);
 
+extern bool g_replaced_default_zone;
+
 // Calls the original implementation of malloc/calloc prior to interception.
 bool UncheckedMallocMac(size_t size, void** result);
 bool UncheckedCallocMac(size_t num_items, size_t size, void** result);
 
 // Intercepts calls to default and purgeable malloc zones. Intercepts Core
 // Foundation and Objective-C allocations.
 // Has no effect on the default malloc zone if the allocator shim already
 // performs that interception.
-void InterceptAllocationsMac();
+BASE_EXPORT void InterceptAllocationsMac();
 }  // namespace allocator
 }  // namespace base
 
 #endif  // BASE_ALLOCATOR_ALLOCATOR_INTERCEPTION_MAC_H_