Add discardable memory emulation for non-android/mac platforms

base/memory/discardable_memory_emulated.cc

Index: base/memory/discardable_memory_emulated.cc
diff --git a/base/memory/discardable_memory_emulated.cc b/base/memory/discardable_memory_emulated.cc
new file mode 100644
index 0000000000000000000000000000000000000000..269012b901036de970e9f5f5d9e8bf45d7e38ab7
--- /dev/null
+++ b/base/memory/discardable_memory_emulated.cc
@@ -0,0 +1,65 @@
+// Copyright 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/memory/discardable_memory_provider.h"
+
+using base::internal::DiscardableMemoryProvider;
+
+namespace base {
+
+// static
+bool DiscardableMemory::SupportedNatively() {
+  return false;
+}
+
+DiscardableMemory::~DiscardableMemory() {
+  if (is_locked_)
+    Unlock();
+  DiscardableMemoryProvider::GetInstance()->Unregister(this);
+}
+
+bool DiscardableMemory::InitializeAndLock(size_t size) {
+  DCHECK(!acquired_memory_);
+
+  DiscardableMemoryProvider::GetInstance()->Register(this, size);
+  size_ = size;
+  return Lock() == DISCARDABLE_MEMORY_PURGED;
+}
+
+LockDiscardableMemoryStatus DiscardableMemory::Lock() {
+  DCHECK(!is_locked_);
+
+  bool purged = false;
+  // This can fail if we have not been registered. That is, it's an error to
+  // |Lock| before calling |InitializeAndLock|.
+  acquired_memory_ = DiscardableMemoryProvider::GetInstance()->Acquire(
+      this, &purged);
+  if (!acquired_memory_)
+    return DISCARDABLE_MEMORY_FAILED;
+
+  memory_ = acquired_memory_.get();
+  is_locked_ = true;
+  return purged ? DISCARDABLE_MEMORY_PURGED : DISCARDABLE_MEMORY_SUCCESS;
+}
+
+void DiscardableMemory::Unlock() {
+  DCHECK(is_locked_);
+  DiscardableMemoryProvider::GetInstance()->Release(
+      this, acquired_memory_.Pass());
+  is_locked_ = false;
+}
+
+// static
+bool DiscardableMemory::PurgeForTestingSupported() {
+  return true;
+}
+
+// static
+void DiscardableMemory::PurgeForTesting() {
+  DiscardableMemoryProvider::GetInstance()->PurgeAll();
+}
+
+}  // namespace base