Allocator shim skeleton + Linux impl behind a build flag

base/allocator/allocator_shim_default_dispatch_to_glibc.cc

Index: base/allocator/allocator_shim_default_dispatch_to_glibc.cc
diff --git a/base/allocator/allocator_shim_default_dispatch_to_glibc.cc b/base/allocator/allocator_shim_default_dispatch_to_glibc.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a9f3c5f502cc0f5d06de98494408e577b3d3d0c4
--- /dev/null
+++ b/base/allocator/allocator_shim_default_dispatch_to_glibc.cc
@@ -0,0 +1,52 @@
+// 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.
+
+#include "base/allocator/allocator_shim.h"
+
+// This translation unit defines a default dispatch for the allocator shim which
+// routes allocations to libc functions.
+// The code here is strongly inspired from tcmalloc's libc_override_glibc.h.
+
+extern "C" {
+void* __libc_malloc(size_t size);
+void* __libc_calloc(size_t n, size_t size);
+void* __libc_realloc(void* address, size_t size);
+void* __libc_memalign(size_t alignment, size_t size);
+void __libc_free(void* ptr);
+}  // extern "C"
+
+namespace {
+
+using base::allocator::AllocatorDispatch;
+
+void* GlibcMalloc(size_t size, const AllocatorDispatch*) {
+  return __libc_malloc(size);
+}
+
+void* GlibcCalloc(size_t n, size_t size, const AllocatorDispatch*) {
+  return __libc_calloc(n, size);
+}
+
+void* GlibcRealloc(void* address, size_t size, const AllocatorDispatch*) {
+  return __libc_realloc(address, size);
+}
+
+void* GlibcMemalign(size_t alignment, size_t size, const AllocatorDispatch*) {
+  return __libc_memalign(alignment, size);
+}
+
+void GlibcFree(void* address, const AllocatorDispatch*) {
+  __libc_free(address);
+}
+
+}  // namespace
+
+const AllocatorDispatch AllocatorDispatch::default_dispatch = {
+    &GlibcMalloc,   /* alloc_function */
+    &GlibcCalloc,   /* alloc_zero_initialized_function */
+    &GlibcMemalign, /* alloc_aligned_function */
+    &GlibcRealloc,  /* realloc_function */
+    &GlibcFree,     /* free_function */
+    nullptr,        /* next */
+};