Caterpillar now generates app.info.js, a metadata script. Resolves #12.

tests/js/polyfills/runtime.polyfill.test.js

 // Copyright 2015 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 87 matching lines @@
     done();
   }
 
   chrome.runtime.getPlatformInfo(callback);
 });
 
 // Check that getPackageDirectoryEntry throws a not implemented error.
 QUnit.test('getPackageDirectoryEntry not implemented', function(assert) {
   assert.throws(chrome.runtime.getPackageDirectoryEntry, 'not implemented');
 });
+
+// Test that id is null.
+QUnit.test('id correct', function(assert) {
+  assert.strictEqual(chrome.runtime.id, null);
+});