Fire null Device Motion events only once.

Source/modules/device_orientation/DeviceMotionController.cpp

Index: Source/modules/device_orientation/DeviceMotionController.cpp
diff --git a/Source/modules/device_orientation/DeviceMotionController.cpp b/Source/modules/device_orientation/DeviceMotionController.cpp
index b001f486f7a6c5c6c7c62bcc7c4384221a598eee..954c7ae59827e276e6ef775548a128d71bbfec8f 100644
--- a/Source/modules/device_orientation/DeviceMotionController.cpp
+++ b/Source/modules/device_orientation/DeviceMotionController.cpp
@@ -28,6 +28,7 @@
 #include "modules/device_orientation/DeviceMotionController.h"
 
 #include "core/dom/Document.h"
+#include "modules/device_orientation/DeviceMotionData.h"
 #include "modules/device_orientation/DeviceMotionDispatcher.h"
 #include "modules/device_orientation/DeviceMotionEvent.h"
 
@@ -82,4 +83,17 @@ void DeviceMotionController::unregisterWithDispatcher()
     DeviceMotionDispatcher::instance().removeDeviceMotionController(this);
 }
 
+bool DeviceMotionController::isNullEvent(Event* event)
+{
+    DeviceMotionEvent* motionEvent = static_cast<DeviceMotionEvent*>(event);

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

How do we know this static_cast is valid?  Can we add some sort of ASSERT to
verify that the type is correct?  For example, we could check the
interfaceName() of the event.

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

The static cast is a bit unfortunate here, but my reasoning for its correctness
is as follows:

The virtual method isNullEvent is only called from
DeviceSensorEventController::dispatchDeviceEvent. For motion,
dispatchDeviceEvent is called from two places, either from
DeviceMotionController::didChangeDeviceMotion or
DeviceSensorEventController::fireDeviceEvent. In the first case the passed event
will be of type motion by definition, in the second case the event will be
fetched by getLastEvent which is an virtual overriden method.

I've added an assert on event->type().

+    DeviceMotionData* data = motionEvent->deviceMotionData();
+    RefPtr<DeviceMotionData::Acceleration> acceleration = data->acceleration();
+    RefPtr<DeviceMotionData::Acceleration> accelerationIncludingGravity = data->accelerationIncludingGravity();
+    RefPtr<DeviceMotionData::RotationRate> rotationRate = data->rotationRate();
+
+    return !acceleration->canProvideX() && !acceleration->canProvideY() && !acceleration->canProvideZ()
+        && !accelerationIncludingGravity->canProvideX() && !accelerationIncludingGravity->canProvideY() && !accelerationIncludingGravity->canProvideZ()
+        && !rotationRate->canProvideAlpha() && !rotationRate->canProvideBeta() && !rotationRate->canProvideGamma();
+}
+
 } // namespace WebCore