Fix handling of null pointers in JS bindings.

mojo/apps/js/test/js_to_cpp_unittest.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.
 
 define('mojo/apps/js/test/js_to_cpp_unittest', [
   'console',
   'mojo/apps/js/test/js_to_cpp.mojom',
   'mojo/public/js/bindings/connection',
   'mojo/public/js/bindings/connector',
   'mojo/public/js/bindings/core',
@@ skipping 11 matching lines @@
     this.cppSide_ = cppSide;
     cppSide.startTest();
   }
 
   JsSideConnection.prototype = Object.create(jsToCpp.JsSideStub.prototype);
 
   JsSideConnection.prototype.ping = function (arg) {
     this.cppSide_.pingResponse();
   };
 
-  JsSideConnection.prototype.echo = function (numIterations, arg) {
+  JsSideConnection.prototype.echo = function (numIterations, list) {
+    var arg = list.item;
     var arg2;
     var dataPipe1;
     var dataPipe2;
     var i;
+    var list;

[Matt Perry, 2014/05/16 18:39:04]

this looks unused

     var messagePipe1;
     var messagePipe2;
 
     // Ensure expected negative values are negative.
     if (arg.si64 > 0)
       arg.si64 = BAD_VALUE;
 
     if (arg.si32 > 0)
       arg.si32 = BAD_VALUE;
 
@@ skipping 16 matching lines @@
       arg2.si64 = -1;
       arg2.si32 = -1;
       arg2.si16 = -1;
       arg2.si8 = -1;
       arg2.name = 'going';
       arg2.data_handle = dataPipe2.consumerHandle;
       arg2.message_handle = messagePipe2.handle1;
 
       writeDataPipe(dataPipe1, senderData);
       writeDataPipe(dataPipe2, senderData);
-      this.cppSide_.echoResponse(arg, arg2);
+
+      var list = new jsToCpp.EchoArgsList();

[Matt Perry, 2014/05/16 18:39:04]

use a different variable name - this one shadows the param name

[Tom Sepez, 2014/05/16 18:57:17]

Yeah, I noticed this soon after posting this. Done.

+      list.next = new jsToCpp.EchoArgsList();
+      list.item = arg2;
+      list.next.item = arg;
+
+      this.cppSide_.echoResponse(list);
 
       core.close(dataPipe1.producerHandle);
       core.close(dataPipe2.producerHandle);
       core.close(messagePipe1.handle0);
       core.close(messagePipe2.handle0);
     }
     this.cppSide_.testFinished();
   };
 
   JsSideConnection.prototype.bitFlip = function (arg) {
@@ skipping 53 matching lines @@
   return function(handle) {
     var i;
     senderData = new Uint8Array(DATA_PIPE_PARAMS.capacityNumBytes);
     for (i = 0; i < senderData.length; ++i)
       senderData[i] = i;
 
     retainedConnection = new connection.Connection(handle, JsSideConnection,
                                                    jsToCpp.CppSideProxy);
   };
 });