Add updateMatrix to fake drawable test

test/unit/extension_video_sensing.js

@@ -87,6 +87,8 @@ const isNearAngle = (actual, expect, optMargin = 10) => (
 // A fake scratch-render drawable that will be used by VideoMotion to restrain
 // the area considered for motion detection in VideoMotion.getLocalMotion
 const fakeDrawable = {
+    updateMatrix () {}, // no-op, since isTouching always returns true
+
     getFastBounds () {
         return {
             left: -120,