Fire null Device Motion events only once.

Source/modules/device_orientation/DeviceOrientationDispatcher.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 16 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "modules/device_orientation/DeviceOrientationDispatcher.h"
 
 #include "modules/device_orientation/DeviceOrientationData.h"
 #include "modules/device_orientation/NewDeviceOrientationController.h"
 #include "public/platform/Platform.h"
+#include "wtf/TemporaryChange.h"
 
 namespace WebCore {
 
 DeviceOrientationDispatcher& DeviceOrientationDispatcher::instance()
 {
     DEFINE_STATIC_LOCAL(DeviceOrientationDispatcher, deviceOrientationDispatcher, ());
     return deviceOrientationDispatcher;
 }
 
 DeviceOrientationDispatcher::DeviceOrientationDispatcher()
@@ skipping 15 matching lines @@
 }
 
 void DeviceOrientationDispatcher::startListening()
 {
     WebKit::Platform::current()->setDeviceOrientationListener(this);
 }
 
 void DeviceOrientationDispatcher::stopListening()
 {
     WebKit::Platform::current()->setDeviceOrientationListener(0);
+    m_lastDeviceOrientationData.clear();
 }
 
 void DeviceOrientationDispatcher::didChangeDeviceOrientation(const WebKit::WebDeviceOrientationData& motion)
 {
     m_lastDeviceOrientationData = DeviceOrientationData::create(motion);
-    bool needsPurge = false;
-    for (size_t i = 0; i < m_controllers.size(); ++i) {
-        if (m_controllers[i])
-            static_cast<NewDeviceOrientationController*>(m_controllers[i])->didChangeDeviceOrientation(m_lastDeviceOrientationData.get());
-        else
-            needsPurge = true;
+
+    {
+        TemporaryChange<bool> changeIsDispatching(m_isDispatching, true);
+        // Don't fire controllers removed or added during event dispatch.
+        size_t size = m_controllers.size();
+        for (size_t i = 0; i < size; ++i) {
+            if (m_controllers[i])
+                static_cast<NewDeviceOrientationController*>(m_controllers[i])->didChangeDeviceOrientation(m_lastDeviceOrientationData.get());
+        }
     }
 
-    if (needsPurge)
+    if (m_needsPurge)
         purgeControllers();
 }
 
 DeviceOrientationData* DeviceOrientationDispatcher::latestDeviceOrientationData()
 {
     return m_lastDeviceOrientationData.get();
 }
 
 } // namespace WebCore