components/metrics: Add runtime memory leak detector

components/metrics/leak_detector/custom_allocator.cc

+// 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.
+
+#include "components/metrics/leak_detector/custom_allocator.h"
+
+#include <stddef.h>
+
+namespace metrics {
+namespace leak_detector {
+
+namespace {
+
+// Wrappers around new and delete.
+void* DefaultAlloc(size_t size) {
+  return new char[size];
+}
+void DefaultFree(void *ptr, size_t /* size */) {
+  delete [] reinterpret_cast<char*>(ptr);
+}
+
+CustomAllocator::AllocFunc g_alloc_func = nullptr;
+CustomAllocator::FreeFunc g_free_func = nullptr;
+
+}  // namespace
+
+// static
+void CustomAllocator::Initialize() {
+  Initialize(&DefaultAlloc, &DefaultFree);
+}
+
+// static
+void CustomAllocator::Initialize(AllocFunc alloc_func, FreeFunc free_func) {
+  g_alloc_func = alloc_func;
+  g_free_func = free_func;
+}
+
+// static
+bool CustomAllocator::Shutdown() {
+  g_alloc_func = nullptr;

[jar (doing other things), 2015/11/14 02:58:36]

I'm curious how this will be done in a race-free manner.

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

Again, see this code:
https://codereview.chromium.org/986503002/diff/1880001/components/metrics/lea...

Any access to LeakDetectorImpl will be guarded by a lock. All other classes are
dependencies of LeakDetectorImpl and will likewise be protected. See class
hierarchy here:
https://docs.google.com/drawings/d/1lp5VVFAOu7vg0aFTCa_4T4AQNh_HPFRGNZr0Tz8i4...

+  g_free_func = nullptr;
+  return true;
+}
+
+// static
+bool CustomAllocator::IsInitialized() {
+  return g_alloc_func && g_free_func;
+}
+
+// static
+void* CustomAllocator::Allocate(size_t size) {
+  return g_alloc_func(size);
+}
+
+// static
+void CustomAllocator::Free(void* ptr, size_t size) {
+  g_free_func(ptr, size);
+}
+
+}  // namespace leak_detector
+}  // namespace metrics