trace fix

Runtime/gestures/mouse_tracking.cs

 
         _TrackedAnnotation _findAnnotation(MouseTrackerAnnotation annotation) {
             if (!this._trackedAnnotations.TryGetValue(annotation, out var trackedAnnotation)) {
-                D.assert(false, "Unable to find annotation $annotation in tracked annotations. " +
+                D.assert(false, () => "Unable to find annotation $annotation in tracked annotations. " +
                                 "Check that attachAnnotation has been called for all annotated layers.");
             }
             

Runtime/rendering/proxy_box.cs

             D.assert(this._onPointerEnter != this._hoverAnnotation.onEnter ||
                      this._onPointerHover != this._hoverAnnotation.onHover ||
                      this._onPointerExit != this._hoverAnnotation.onExit,
-                "Shouldn't call _updateAnnotations if nothing has changed.");
+                () => "Shouldn't call _updateAnnotations if nothing has changed.");
 
             if (this._hoverAnnotation != null && this.attached) {
                 RendererBinding.instance.mouseTracker.detachAnnotation(this._hoverAnnotation);