chore(ci): re-enable tests on Windows (#5637)

* chore: Add Windows to Travis

This commit runs the unit tests on Windows.

There are two tests failing on Windows that we skip.

I spoke to Mathias B and we agreed to
defer debugging this for now in favour of getting tests running on
Windows. But we didn't want to ignore it forever, hence giving the test
a date at which it will start to fail.

mocha-config/puppeteer-unit-tests.js

@@ -1,8 +1,31 @@
+/**
+ * Copyright 2020 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,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const os = require('os');
 const base = require('./base');
 
+const longerTimeoutRequired = process.env.PUPPETEER_PRODUCT === 'firefox' || os.platform() === 'win32';
+
+const timeout = longerTimeoutRequired ? 25 * 1000 : 10 * 1000;
+
+console.log('Mocha config: Timeout set to', timeout / 1000, 'seconds');
+
 module.exports = {
   ...base,
   file: ['./test/mocha-utils.js'],
   spec: 'test/*.spec.js',
-  timeout: process.env.PUPPETEER_PRODUCT === 'firefox' ? 15 * 1000 : 10 * 1000,
+  timeout,
 };