Make InsertAllocatorDispatch thread safe.

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 68 matching lines @@
 };
 
 // When true makes malloc behave like new, w.r.t calling the new_handler if
 // the allocation fails (see set_new_mode() in Windows).
 BASE_EXPORT void SetCallNewHandlerOnMallocFailure(bool value);
 
 // Allocates |size| bytes or returns nullptr. It does NOT call the new_handler,
 // regardless of SetCallNewHandlerOnMallocFailure().
 BASE_EXPORT void* UncheckedAlloc(size_t size);
 
-// Inserts |dispatch| in front of the allocator chain. This method is NOT
+// Inserts |dispatch| in front of the allocator chain. This method is
 // thread-safe w.r.t concurrent invocations of InsertAllocatorDispatch().
-// The callers have the responsibility of linearizing the changes to the chain
-// (or more likely call these always on the same thread).
+// The callers have responsibility for inserting a single dispatch no more
+// than once.
 BASE_EXPORT void InsertAllocatorDispatch(AllocatorDispatch* dispatch);
 
 // 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_