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

Source/core/frame/DeviceEventControllerBase.cpp

+// 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.
+
+#include "config.h"
+#include "core/frame/DeviceEventControllerBase.h"
+
+#include "core/page/Page.h"
+
+namespace WebCore {
+
+DeviceEventControllerBase::DeviceEventControllerBase(Page* page)
+    : PageLifecycleObserver(page)
+    , m_hasEventListener(false)
+    , m_isActive(false)
+    , m_timer(this, &DeviceEventControllerBase::oneShotCallback)
+{
+}
+
+DeviceEventControllerBase::~DeviceEventControllerBase()
+{
+}
+
+void DeviceEventControllerBase::oneShotCallback(Timer<DeviceEventControllerBase>* timer)
+{
+    ASSERT_UNUSED(timer, timer == &m_timer);
+    ASSERT(hasLastData());
+    ASSERT(!m_timer.isActive());
+
+    didUpdateData();
+}
+
+void DeviceEventControllerBase::startUpdating()
+{
+    if (m_isActive)
+        return;
+
+    if (hasLastData() && !m_timer.isActive()) {
+        // Make sure to fire the data as soon as possible.
+        m_timer.startOneShot(0, FROM_HERE);
+    }
+
+    registerWithDispatcher();
+    m_isActive = true;
+}
+
+void DeviceEventControllerBase::stopUpdating()
+{
+    if (!m_isActive)
+        return;
+
+    if (m_timer.isActive())
+        m_timer.stop();
+
+    unregisterWithDispatcher();
+    m_isActive = false;
+}
+
+void DeviceEventControllerBase::pageVisibilityChanged()
+{
+    if (!m_hasEventListener)
+        return;
+
+    if (page()->visibilityState() == PageVisibilityStateVisible)
+        startUpdating();
+    else
+        stopUpdating();
+}
+
+} // namespace WebCore