Change mojo JS bindings to expose a handle object, which is Closed when garbage

mojo/bindings/js/core_unittests.js

 // Copyright 2013 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([
     "gin/test/expect",
     "mojo/bindings/js/core",
-  ], function(expect, core) {
+    "gc",
+  ], function(expect, core, gc) {
   runWithMessagePipe(testNop);
   runWithMessagePipe(testReadAndWriteMessage);
   runWithDataPipe(testNop);
   runWithDataPipe(testReadAndWriteDataPipe);
+  gc.collectGarbage();  // should not crash
   this.result = "PASS";
 
   function runWithMessagePipe(test) {
     var pipe = core.createMessagePipe();
 
     test(pipe);
 
     expect(core.close(pipe.handle0)).toBe(core.RESULT_OK);
     expect(core.close(pipe.handle1)).toBe(core.RESULT_OK);
   }
@@ skipping 57 matching lines @@
 
     expect(read.result).toBe(core.RESULT_OK);
     expect(read.buffer.byteLength).toBe(42);
 
     var memory = new Uint8Array(read.buffer);
     for (var i = 0; i < memory.length; ++i)
       expect(memory[i]).toBe((i * i) & 0xFF);
   }
 
 });