base: Refactor DiscardableMemoryProvider to build and be tested on all platforms.

base/memory/discardable_memory_linux.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_emulated.h"
+
+namespace base {
+
+// static
+bool DiscardableMemory::SupportedNatively() {
+  return false;
+}
+
+// static
+scoped_ptr<DiscardableMemory> DiscardableMemory::CreateLockedMemory(
+    size_t size) {
+  scoped_ptr<internal::DiscardableMemoryEmulated> memory(
+      new internal::DiscardableMemoryEmulated(size));
+  if (!memory->Initialize())
+    return scoped_ptr<DiscardableMemory>();
+
+  return memory.PassAs<DiscardableMemory>();
+}
+
+// static
+bool DiscardableMemory::PurgeForTestingSupported() {
+  return true;
+}
+
+// static
+void DiscardableMemory::PurgeForTesting() {
+  internal::DiscardableMemoryEmulated::PurgeForTesting();
+}
+
+}  // namespace base