Tolerate that CMD_SYNC does not exist (per U2F spec).

chrome/browser/resources/cryptotoken/gnubby.js

 // Copyright 2014 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.
 
 /**
  * @fileoverview Provides a client view of a gnubby, aka USB security key.
  */
 'use strict';
 
 /**
@@ skipping 505 matching lines @@
         (f.length == 7 || /* fw pre-0.2.1 bug: does not echo sentinel */
          f[7] == self.synccnt));
   }
 
   function syncCompletionAction(rc, opt_frame) {
     if (rc) console.warn(UTIL_fmt('sync failed: ' + rc));
     returnValue(rc);
   }
 
   function sendInitSentinel() {
-    var cid = Gnubby.BROADCAST_CID;
+    var cid = self.cid;
+    if (cid == Gnubby.defaultChannelId_(self.gnubbyInstance, self.which)) {
+      cid = Gnubby.BROADCAST_CID;
+    }
     var cmd = GnubbyDevice.CMD_INIT;
     self.dev.queueCommand(cid, cmd, nonce);
   }
 
   function initSentinelEquals(f) {
     return (f[4] == GnubbyDevice.CMD_INIT &&
         f.length >= nonce.length + 7 &&
         UTIL_equalArrays(f.subarray(7, nonce.length + 7), nonce));
   }
 
@@ skipping 84 matching lines @@
     sentinelEquals = initSentinelEquals;
     completionAction = initCompletionAction;
   }
 
   function setSync() {
     sendSentinel = sendSyncSentinel;
     sentinelEquals = syncSentinelEquals;
     completionAction = syncCompletionAction;
   }
 
-  if (Gnubby.gnubbies_.isSharedAccess(this.which) &&
-      this.cid == Gnubby.defaultChannelId_(this.gnubbyInstance, this.which)) {
+  if (Gnubby.gnubbies_.isSharedAccess(this.which)) {
     setInit();
   } else {
     setSync();
   }
   timeoutLoop();
 };
 
 /** Short timeout value in seconds */
 Gnubby.SHORT_TIMEOUT = 1;
 /** Normal timeout value in seconds */
@@ skipping 141 matching lines @@
       }
     }
     // Warn on errors other than waiting for touch, wrong data, and
     // unrecognized command.
     if (rc != 0x6985 && rc != 0x6a80 && rc != 0x6d00) {
       console.warn(UTIL_fmt('apduReply_ fail: ' + rc.toString(16)));
     }
     cb(rc);
   });
 };