Start refactoring Windows allocator shim in prep for hooking in generic allocator shim on Windows.

base/allocator/winheap_stubs_win.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.
+
+// This code should move into the default Windows shim once the win-specific
+// allocation shim has been removed, and the generic shim has becaome the
+// default.
+
+#include "winheap_stubs_win.h"
+
+#include <limits.h>
+#include <malloc.h>
+#include <new.h>
+#include <windows.h>
+
+namespace base {
+namespace allocator {
+
+bool g_is_win_shim_layer_initialized = false;
+
+namespace {
+
+const size_t kWindowsPageSize = 4096;
+const size_t kMaxWindowsAllocation = INT_MAX - kWindowsPageSize;
+
+inline HANDLE get_heap_handle() {
+  return reinterpret_cast<HANDLE>(_get_heap_handle());
+}
+
+}  // namespace
+
+void* WinHeapMalloc(size_t size) {
+  if (size < kMaxWindowsAllocation)
+    return HeapAlloc(get_heap_handle(), 0, size);
+  return nullptr;
+}
+
+void WinHeapFree(void* size) {
+  HeapFree(get_heap_handle(), 0, size);
+}
+
+void* WinHeapRealloc(void* ptr, size_t size) {
+  if (!ptr)
+    return WinHeapMalloc(size);
+  if (!size) {
+    WinHeapFree(ptr);
+    return nullptr;
+  }
+  if (size < kMaxWindowsAllocation)
+    return HeapReAlloc(get_heap_handle(), 0, ptr, size);
+  return nullptr;
+}
+
+// Call the new handler, if one has been set.
+// Returns true on successfully calling the handler, false otherwise.
+bool WinCallNewHandler(size_t size) {
+#if !defined(_HAS_EXCEPTIONS) || _HAS_EXCEPTIONS
+#error "Exceptions in allocator shim are not supported!"
+#endif  // defined(_HAS_EXCEPTIONS) && !_HAS_EXCEPTIONS
+  // Get the current new handler.
+  _PNH nh = _query_new_handler();
+  if (!nh)
+    return false;
+  // Since exceptions are disabled, we don't really know if new_handler
+  // failed.  Assume it will abort if it fails.
+  return nh(size) ? true : false;
+}
+
+}  // namespace allocator
+}  // namespace base