Missed a constructor in #6632.

Author: emackey

Source/Scene/ClassificationModel.js

@@ -88,7 +88,7 @@ define([
     ///////////////////////////////////////////////////////////////////////////
 
     /**
-     * A 3D model for classifying other 3D assets based on glTF, the runtime asset format for WebGL, OpenGL ES, and OpenGL.
+     * A 3D model for classifying other 3D assets based on glTF, the runtime 3D asset format.
      * This is a special case when a model of a 3D tileset becomes a classifier when setting {@link Cesium3DTileset#classificationType}.
      *
      * @alias ClassificationModel

Source/Scene/Instanced3DModel3DTileContent.js

@@ -21,6 +21,7 @@ define([
         '../Core/Transforms',
         '../Core/TranslationRotationScale',
         '../Renderer/Pass',
+        './Axis',
         './Cesium3DTileBatchTable',
         './Cesium3DTileFeature',
         './Cesium3DTileFeatureTable',
@@ -48,6 +49,7 @@ define([
         Transforms,
         TranslationRotationScale,
         Pass,
+        Axis,
         Cesium3DTileBatchTable,
         Cesium3DTileFeature,
         Cesium3DTileFeatureTable,
@@ -281,6 +283,7 @@ define([
             basePath : undefined,
             incrementallyLoadTextures : false,
             upAxis : content._tileset._gltfUpAxis,
+            forwardAxis : Axis.X,
             opaquePass : Pass.CESIUM_3D_TILE, // Draw opaque portions during the 3D Tiles pass
             pickIdLoaded : getPickIdCallback(content)
         };