[Not for review] Discardable memory emulation

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/logging.h"
-
 namespace base {
 
-DiscardableMemory::DiscardableMemory()
-    : memory_(NULL),
-      size_(0),
-      is_locked_(false)
-#if defined(OS_ANDROID)
-      , fd_(-1)
-#endif  // OS_ANDROID
-      {
-  DCHECK(Supported());
-}
+#if !defined(DISCARDABLE_MEMORY_SUPPORTED_NATIVELY)
+static DiscardableMemoryProvider* s_factory = NULL;
 
-void* DiscardableMemory::Memory() const {
-  DCHECK(is_locked_);
-  return memory_;
-}
-
-// Stub implementations for platforms that don't support discardable memory.
-
-#if !defined(OS_ANDROID) && !defined(OS_MACOSX)
-
-DiscardableMemory::~DiscardableMemory() {
-  NOTIMPLEMENTED();
+// static
+DiscardableMemoryProvider* DiscardableMemoryProvider::GetInstance() {
+  return s_factory;
 }
 
 // static
-bool DiscardableMemory::Supported() {
-  return false;
+void DiscardableMemoryProvider::SetInstance(
+    DiscardableMemoryProvider* factory) {
+  s_factory = factory;
+}
+#endif
+
+DiscardableMemory::~DiscardableMemory() {
 }
 
-bool DiscardableMemory::InitializeAndLock(size_t size) {
-  NOTIMPLEMENTED();
-  return false;
-}
-
-LockDiscardableMemoryStatus DiscardableMemory::Lock() {
-  NOTIMPLEMENTED();
-  return DISCARDABLE_MEMORY_FAILED;
-}
-
-void DiscardableMemory::Unlock() {
-  NOTIMPLEMENTED();
-}
-
-// static
-bool DiscardableMemory::PurgeForTestingSupported() {
-  return false;
-}
-
-// static
-void DiscardableMemory::PurgeForTesting() {
-  NOTIMPLEMENTED();
-}
-
-#endif  // OS_*
-
 }  // namespace base