Add discardable memory emulation for non-android/mac platforms

base/memory/discardable_memory.cc

-// Copyright (c) 2013 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/memory/discardable_memory.h"
-
-#include "base/compiler_specific.h"
-#include "base/logging.h"
-
-namespace base {
-
-// Stub implementations for platforms that don't support discardable memory.
-
-#if !defined(OS_ANDROID) && !defined(OS_MACOSX)
-
-// static
-bool DiscardableMemory::Supported() {
-  return false;
-}
-
-// static
-scoped_ptr<DiscardableMemory> DiscardableMemory::CreateLockedMemory(
-    size_t size) {
-  return scoped_ptr<DiscardableMemory>();
-}
-
-// static
-bool DiscardableMemory::PurgeForTestingSupported() {
-  return false;
-}
-
-// static
-void DiscardableMemory::PurgeForTesting() {
-  NOTIMPLEMENTED();
-}
-
-#endif  // OS_*
-
-}  // namespace base