Fire null Device Motion events only once.

Source/modules/device_orientation/DeviceSensorEventController.cpp

Index: Source/modules/device_orientation/DeviceSensorEventController.cpp
diff --git a/Source/modules/device_orientation/DeviceSensorEventController.cpp b/Source/modules/device_orientation/DeviceSensorEventController.cpp
index fc5ae617122dcea135e2b236f3ea363db7443713..4b2efb308ed402c00ab611d592cc1795aa155f1a 100644
--- a/Source/modules/device_orientation/DeviceSensorEventController.cpp
+++ b/Source/modules/device_orientation/DeviceSensorEventController.cpp
@@ -35,6 +35,7 @@ namespace WebCore {
 DeviceSensorEventController::DeviceSensorEventController(Document* document)
     : m_document(document)
     , m_isActive(false)
+    , m_needsCheckingNullEvents(true)
     , m_timer(this, &DeviceSensorEventController::fireDeviceEvent)
 {
 }
@@ -60,6 +61,13 @@ void DeviceSensorEventController::dispatchDeviceEvent(PassRefPtr<Event> prpEvent
         && !m_document->activeDOMObjectsAreSuspended()
         && !m_document->activeDOMObjectsAreStopped())
         m_document->domWindow()->dispatchEvent(event);
+
+    if (m_needsCheckingNullEvents) {
+        if (isNullEvent(event.get()))
+            stopUpdating();
+        else
+            m_needsCheckingNullEvents = false;

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

We still need to check for null events in the stopUpdating branch?

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

If you mean we are not setting m_needsCheckingNullEvents in the stopUpdating
case that is intentional. If javascript does addDeviceListenter twice one after
each other then each time we'll fire once and unregister.

m_needsCheckingNullEvents flag is meant to optimize the case where the events
are not null, once we receive one non-null event we can be certain there will be
no null-events in the future.

+    }
 }
 
 void DeviceSensorEventController::startUpdating()
@@ -67,13 +75,13 @@ void DeviceSensorEventController::startUpdating()
     if (m_isActive)
         return;
 
-    registerWithDispatcher();
-    m_isActive = true;
-
     if (hasLastData() && !m_timer.isActive()) {
         // Make sure to fire the device motion data as soon as possible.
         m_timer.startOneShot(0);
     }
+
+    registerWithDispatcher();
+    m_isActive = true;
 }
 
 void DeviceSensorEventController::stopUpdating()
@@ -81,6 +89,9 @@ void DeviceSensorEventController::stopUpdating()
     if (!m_isActive)
         return;
 
+    if (m_timer.isActive())
+        m_timer.stop();
+
     unregisterWithDispatcher();
     m_isActive = false;
 }