Bug 909889 - Add guards around drag property access in CrossSlide. r=mbrubeck

browser/metro/modules/CrossSlide.jsm

@@ -240,14 +240,20 @@ CrossSlideHandler.prototype = {
    */
   _fireProgressEvent: function CrossSliding_fireEvent(aState, aEvent) {
     if (!this.drag)
-        return;
+      return;
     let event = this.node.ownerDocument.createEvent("Events");
-    let crossAxis = this.drag.crossAxis;
+    let crossAxisName = this.drag.crossAxis;
     event.initEvent("MozCrossSliding", true, true);
     event.crossSlidingState = aState;
-    event.position = this.drag.position;
-    event.direction = this.drag.crossAxis;
-    event.delta = this.drag.position[crossAxis] - this.drag.origin[crossAxis];
+    if ('position' in this.drag) {
+      event.position = this.drag.position;
+      if (crossAxisName) {
+        event.direction = crossAxisName;
+        if('origin' in this.drag) {
+          event.delta = this.drag.position[crossAxisName] - this.drag.origin[crossAxisName];
+        }
+      }
+    }
     aEvent.target.dispatchEvent(event);
   },