Process null capabilities as a capability fetch failure.

chrome/browser/resources/print_preview/data/destination_store.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 cr.define('print_preview', function() {
   'use strict';
 
   /**
    * A data store that stores destinations and dispatches events when the data
    * store changes.
@@ skipping 1525 matching lines @@
     /**
      * Called when the native layer retrieves the capabilities for the selected
      * local destination. Updates the destination with new capabilities if the
      * destination already exists, otherwise it creates a new destination and
      * then updates its capabilities.
      * @param {Event} event Contains the capabilities of the local print
      *     destination.
      * @private
      */
     onLocalDestinationCapabilitiesSet_: function(event) {
+      var rawCapabilities = event.settingsInfo.capabilities;
+      assert(rawCapabilities);
+
       var destinationId = event.settingsInfo['printerId'];
       var printerName = event.settingsInfo['printerName'];
       var printerDescription = event.settingsInfo['printerDescription'];
       // PDF is special since we don't need to query the device for
       // capabilities.
       var origin = destinationId ==
           print_preview.Destination.GooglePromotedId.SAVE_AS_PDF ?
           print_preview.Destination.Origin.LOCAL : this.platformOrigin_;
       var key = this.getDestinationKey_(
           origin,
           destinationId,
           '');
       var destination = this.destinationMap_[key];
       var capabilities = DestinationStore.localizeCapabilities_(
-          event.settingsInfo.capabilities);
+          rawCapabilities);

[dpapad, 2017/05/02 00:07:41]

If we already assert in native_layer.js before triggering the CAPABILITIES_SET
event, this assertion here is redundant. Can we stick with an assertion either
here or in native_layer.js but not in both?

[skau, 2017/05/02 01:52:47]

Done.

       // Special case for PDF printer (until local printers capabilities are
       // reported in CDD format too).
       if (destinationId ==
           print_preview.Destination.GooglePromotedId.SAVE_AS_PDF) {
         if (destination) {
           destination.capabilities = capabilities;
         }
       } else {
         if (destination) {
           // In case there were multiple capabilities request for this local
@@ skipping 203 matching lines @@
       return this.getDestinationKey_(
           destination.origin, destination.id, destination.account);
     }
   };
 
   // Export
   return {
     DestinationStore: DestinationStore
   };
 });