Entertain the compiler

src/ol/renderer/canvas/layer.js

@@ -78,7 +78,7 @@ ol.renderer.canvas.Layer.prototype.composeFrame = function(frameState, layerStat
     var extent = layerState.extent;
     var clipped = extent !== undefined;
     if (clipped) {
-      this.clip(context, frameState, extent);
+      this.clip(context, frameState, /** @type {ol.Extent} */ (extent));
     }
 
     var imageTransform = this.getImageTransform();

src/ol/renderer/canvas/vectorlayer.js

@@ -89,7 +89,7 @@ ol.renderer.canvas.VectorLayer.prototype.composeFrame = function(frameState, lay
   var clipExtent = layerState.extent;
   var clipped = clipExtent !== undefined;
   if (clipped) {
-    this.clip(context, frameState, clipExtent);
+    this.clip(context, frameState,  /** @type {ol.Extent} */ (clipExtent));
   }
   var replayGroup = this.replayGroup_;
   if (replayGroup && !replayGroup.isEmpty()) {

src/ol/renderer/canvas/vectortilelayer.js

@@ -77,7 +77,7 @@ ol.renderer.canvas.VectorTileLayer.prototype.composeFrame = function(
   var extent = layerState.extent;
   var clipped = extent !== undefined;
   if (clipped) {
-    this.clip(context, frameState, extent);
+    this.clip(context, frameState,  /** @type {ol.Extent} */ (extent));
   }
 
   var renderMode = this.getLayer().getRenderMode();