Generalize and refactor DeviceSensorEvent* architecture to support multi-event type targets.

Source/core/frame/DeviceEventControllerBase.h

+// Copyright 2014 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 DeviceEventControllerBase_h
+#define DeviceEventControllerBase_h
+
+#include "core/page/PageLifecycleObserver.h"
+#include "platform/Timer.h"
+
+namespace WebCore {
+
+// Base controller class for registering controllers with a dispatcher.
+// It watches page visibility and calls stopUpdating when page is not visible.
+// It provides a didUpdateData() callback method which is called when new data
+// it available.
+class DeviceEventControllerBase : public PageLifecycleObserver {
+public:
+    void startUpdating();
+    void stopUpdating();
+
+    // This is called when new data becomes available.
+    virtual void didUpdateData() = 0;
+
+protected:
+    explicit DeviceEventControllerBase(Page*);
+    virtual ~DeviceEventControllerBase();
+
+    virtual void registerWithDispatcher() = 0;
+    virtual void unregisterWithDispatcher() = 0;
+
+    // When true initiates a one-shot didUpdateData() when startUpdating() is called.
+    virtual bool hasLastData() = 0;
+
+    bool m_hasEventListener;
+
+private:
+    // Inherited from PageLifecycleObserver.
+    virtual void pageVisibilityChanged() OVERRIDE FINAL;
+
+    void oneShotCallback(Timer<DeviceEventControllerBase>*);
+
+    bool m_isActive;
+    Timer<DeviceEventControllerBase> m_timer;
+};
+
+} // namespace WebCore
+
+#endif // DeviceEventControllerBase_h