Add MemoryPurgeController

Source/platform/MemoryPurgeController.cpp

+// Copyright 2015 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 "config.h"
+#include "platform/MemoryPurgeController.h"
+
+#include "public/platform/Platform.h"
+
+namespace blink {
+
+MemoryPurgeController::MemoryPurgeController()
+    : m_deviceKind(Platform::current()->isLowEndDeviceMode() ? DeviceKind::LowEnd : DeviceKind::NotSpecified)
+{
+}
+
+void MemoryPurgeController::pageBecameVisible()
+{
+}
+
+void MemoryPurgeController::pageBecameHidden()
+{
+    // TODO(bashi): Invoke this few seconds later.
+    purgeMemory(MemoryPurgeMode::InactiveTab);
+}
+
+void MemoryPurgeController::purgeMemory(MemoryPurgeMode purgeMode)
+{
+    for (auto& client : m_clients)
+        client->purgeMemory(purgeMode, m_deviceKind);
+}
+
+DEFINE_TRACE(MemoryPurgeController)
+{
+#if ENABLE(OILPAN)
+    visitor->trace(m_clients);
+#endif
+}
+
+} // namespace blink