Introduce allocator shim for Android

base/allocator/allocator_shim_default_dispatch_to_linker_wrapped_symbols.cc

+// 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 the original libc functions when using the link-time
+// -Wl,-wrap,malloc approach (see README.md).
+// The __real_X functions here are special symbols that the linker will relocate
+// against the real "X" undefined symbol, so that __real_malloc becomes the
+// equivalent of what an undefined malloc symbol reference would have been.
+// This is the counterpart of allocator_shim_override_linker_wrapped_symbols.h,
+// which routes the __wrap_X functions into the shim.
+
+extern "C" {
+void* __real_malloc(size_t);
+void* __real_calloc(size_t, size_t);
+void* __real_realloc(void*, size_t);
+void* __real_memalign(size_t, size_t);
+void* __real_free(void*);
+}  // extern "C"
+
+namespace {
+
+using base::allocator::AllocatorDispatch;
+
+void* RealMalloc(const AllocatorDispatch*, size_t size) {
+  return __real_malloc(size);
+}
+
+void* RealCalloc(const AllocatorDispatch*, size_t n, size_t size) {
+  return __real_calloc(n, size);
+}
+
+void* RealRealloc(const AllocatorDispatch*, void* address, size_t size) {
+  return __real_realloc(address, size);
+}
+
+void* RealMemalign(const AllocatorDispatch*, size_t alignment, size_t size) {
+  return __real_memalign(alignment, size);
+}
+
+void RealFree(const AllocatorDispatch*, void* address) {
+  __real_free(address);
+}
+
+}  // namespace
+
+const AllocatorDispatch AllocatorDispatch::default_dispatch = {
+    &RealMalloc,   /* alloc_function */
+    &RealCalloc,   /* alloc_zero_initialized_function */
+    &RealMemalign, /* alloc_aligned_function */
+    &RealRealloc,  /* realloc_function */
+    &RealFree,     /* free_function */
+    nullptr,       /* next */
+};