Add MemoryPurgeController

Source/platform/MemoryPurgeController.h

+// 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.
+
+#ifndef MemoryPurgeController_h
+#define MemoryPurgeController_h
+
+#include "wtf/HashSet.h"
+
+namespace blink {
+
+enum MemoryPurgeMode {
+    // The tab contains the webview went to background
+    Inactive,

[dcheng, 2015/08/21 15:04:19]

Suggestion: we should prefer enum class for both of these (Inactive is a pretty
generic name)

[bashi, 2015/08/25 02:34:23]

Done.

+    // TODO(bashi): Add more modes as needed.
+};
+
+enum DeviceKind {

[dcheng, 2015/08/21 15:04:19]

Ditto: NotSpecified is pretty generic.

[bashi, 2015/08/25 02:34:23]

Done.

+    NotSpecified,
+    LowEnd,
+};
+
+// TODO(bashi): Make MemoryPurgeEventListener garbage collected.
+class MemoryPurgeEventListener {
+public:
+    // MemoryPurgeController invokes this callback when a memory purge event
+    // has occurred.
+    virtual void purgeMemory(MemoryPurgeMode, DeviceKind) = 0;
+};
+
+class MemoryPurgeController {
+public:
+    MemoryPurgeController();
+
+    void addListener(MemoryPurgeEventListener* listener) { m_listeners.add(listener); }
+    void removeListener(MemoryPurgeEventListener* listener) { m_listeners.remove(listener); }
+
+    // Called several seconds after the tab went to background.
+    void didBecomeInactive();
+
+private:
+    void purgeMemory(MemoryPurgeMode);
+
+    HashSet<MemoryPurgeEventListener*> m_listeners;
+    DeviceKind m_deviceKind;
+};
+
+} // namespace blink
+
+#endif // MemoryPurgeController_h
+