Fire null Device Motion events only once.

Source/modules/device_orientation/DeviceMotionDispatcher.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 51 matching lines @@
 }
 
 void DeviceMotionDispatcher::startListening()
 {
     WebKit::Platform::current()->setDeviceMotionListener(this);
 }
 
 void DeviceMotionDispatcher::stopListening()
 {
     WebKit::Platform::current()->setDeviceMotionListener(0);
+    m_lastDeviceMotionData.clear();
 }
 
 void DeviceMotionDispatcher::didChangeDeviceMotion(const WebKit::WebDeviceMotionData& motion)
 {
     m_lastDeviceMotionData = DeviceMotionData::create(motion);
-    bool needsPurge = false;
-    for (size_t i = 0; i < m_controllers.size(); ++i) {
+
+    m_isDispatching = true;

[abarth-chromium, 2013/07/31 00:56:19]

Consider using TemporaryChange rather than manually twiddling this flag.

[timvolodine, 2013/07/31 13:59:00]

Done.

+    // Don't fire controllers removed or added during event dispatch.
+    size_t end = m_controllers.size();

[abarth-chromium, 2013/07/31 00:56:19]

end -> length or size

We use the term |end| to refer to iterators, and this is an index not an
iterator.

[timvolodine, 2013/07/31 13:59:00]

changed to size.
Actually I was basing myself on EventTarget::fireEventListeners which does a
similar dispatch and uses |end| to refer to an index as well..

+    for (size_t i = 0; i < end; ++i) {
         if (m_controllers[i])
             static_cast<DeviceMotionController*>(m_controllers[i])->didChangeDeviceMotion(m_lastDeviceMotionData.get());
-        else
-            needsPurge = true;
     }
+    m_isDispatching = false;
 
-    if (needsPurge)
+    if (m_needsPurge)
         purgeControllers();
 }
 
 DeviceMotionData* DeviceMotionDispatcher::latestDeviceMotionData()
 {
     return m_lastDeviceMotionData.get();
 }
 
 } // namespace WebCore