components/metrics: Add runtime memory leak detector

components/metrics/leak_detector/custom_allocator.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 COMPONENTS_METRICS_LEAK_DETECTOR_CUSTOM_ALLOCATOR_H_
+#define COMPONENTS_METRICS_LEAK_DETECTOR_CUSTOM_ALLOCATOR_H_
+
+#include <stddef.h>
+
+#include <type_traits>
+
+namespace metrics {
+namespace leak_detector {
+
+// Custom allocator class to be passed to STLAllocator as a template argument.
+//
+// By default, CustomAllocator uses the default allocator (new/delete), but the
+// caller of Initialize ()can provide a pair of alternative alloc/ free
+// functions to use as an external allocator.

[jar (doing other things), 2015/11/14 02:58:37]

I'm not yet clear how you "hook in," but how do you prevent your custom
allocator from being instrumented (recording stats recursively in your leak
analyzer)?

[Simon Que, 2015/11/17 00:28:48]

It was originally included in this CL, but since it's not being used anywhere,
I've deleted it. Here it is from a previous patch set:
https://codereview.chromium.org/986503002/diff/1880001/components/metrics/lea...

See "InternalAlloc" and "MallocHookDisabler" -- the tcmalloc hooks are removed
to do the allocation, and then reinstated when done.

This may or may not generate a lot of overhead but I also plan to add a local
allocator in a subsequent CL to reduce the number of allocs/frees along this
path. I already have it written up and it is much more efficient than the
LowLevelAlloc used in tcmalloc.

+//
+// This is a stateless class, but there is static data within the module that
+// needs to be created and deleted.
+class CustomAllocator {
+ public:
+  using AllocFunc = std::add_pointer<void*(size_t)>::type;
+  using FreeFunc = std::add_pointer<void(void*, size_t)>::type;
+
+  // Initialize CustomAllocator to use the default allocator.
+  static void Initialize();
+
+  // Initialize CustomAllocator to use the given alloc/free functions.
+  static void Initialize(AllocFunc alloc_func, FreeFunc free_func);
+
+  // Performs any cleanup required, e.g. unset custom functions. Returns true
+  // on success or false if something failed.
+  static bool Shutdown();
+
+  static bool IsInitialized();
+
+  // These functions must match the specifications in STLAllocator.
+  static void* Allocate(size_t size);
+  static void Free(void* ptr, size_t size);
+};
+
+}  // namespace leak_detector
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_LEAK_DETECTOR_CUSTOM_ALLOCATOR_H_