Fire null Device Motion events only once.

LayoutTests/fast/dom/DeviceMotion/add-during-dispatch-expected.txt

Index: LayoutTests/fast/dom/DeviceMotion/add-during-dispatch-expected.txt
diff --git a/LayoutTests/fast/dom/DeviceMotion/add-during-dispatch-expected.txt b/LayoutTests/fast/dom/DeviceMotion/add-during-dispatch-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..adf411c7a874fa572788ce3b1706a5e89c209bd0
--- /dev/null
+++ b/LayoutTests/fast/dom/DeviceMotion/add-during-dispatch-expected.txt
@@ -0,0 +1,20 @@
+Test no fire listeners added during event dispatch.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS deviceMotionEvent.acceleration.x is mockEvent.accelerationX
+PASS deviceMotionEvent.acceleration.y is mockEvent.accelerationY
+PASS deviceMotionEvent.acceleration.z is mockEvent.accelerationZ
+PASS deviceMotionEvent.accelerationIncludingGravity.x is mockEvent.accelerationIncludingGravityX
+PASS deviceMotionEvent.accelerationIncludingGravity.y is mockEvent.accelerationIncludingGravityY
+PASS deviceMotionEvent.accelerationIncludingGravity.z is mockEvent.accelerationIncludingGravityZ
+PASS deviceMotionEvent.rotationRate.alpha is mockEvent.rotationRateAlpha
+PASS deviceMotionEvent.rotationRate.beta is mockEvent.rotationRateBeta
+PASS deviceMotionEvent.rotationRate.gamma is mockEvent.rotationRateGamma
+PASS deviceMotionEvent.interval is mockEvent.interval
+PASS numSecondListenerCalls is 1
+PASS successfullyParsed is true
+
+TEST COMPLETE
+