feat: introduce puppeteer-firefox (#3628)

This adds a proof-of-concept of `puppeteer-firefox`.
This consists of two parts:
- `//experimental/juggler` - patches to apply to Firefox.
- `//experimental/puppeteer-firefox` - front-end code to
be merged with Puppeteer.

As things become more stable, we'll gradually move it out of
the experimental folder.

experimental/puppeteer-firefox/test/test.js

@@ -0,0 +1,80 @@
+/**
+ * Copyright 2018 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 path = require('path');
+const {TestServer} = require('@pptr/testserver');
+const {TestRunner, Reporter} = require('@pptr/testrunner');
+
+let parallel = 1;
+const parallelArgIndex = process.argv.indexOf('-j');
+if (parallelArgIndex !== -1)
+  parallel = parseInt(process.argv[parallelArgIndex + 1], 10);
+require('events').defaultMaxListeners *= parallel;
+
+let timeout = 10000;
+if (!isNaN(process.env.TIMEOUT))
+  timeout = parseInt(process.env.TIMEOUT, 10);
+const testRunner = new TestRunner({timeout, parallel});
+
+console.log('Testing on Node', process.version);
+
+testRunner.beforeAll(async state => {
+  const assetsPath = path.join(__dirname, 'assets');
+
+  const port = 8907 + state.parallelIndex * 2;
+  state.server = await TestServer.create(assetsPath, port);
+  state.server.PORT = port;
+  state.server.PREFIX = `http://localhost:${port}`;
+  state.server.EMPTY_PAGE = `http://localhost:${port}/empty.html`;
+  state.server.EMPTY_PAGE2 = `http://localhost:${port}/empty2.html`;
+
+  const httpsPort = port + 1;
+  state.httpsServer = await TestServer.createHTTPS(assetsPath, httpsPort);
+  state.httpsServer.PORT = httpsPort;
+  state.httpsServer.PREFIX = `https://localhost:${httpsPort}`;
+  state.httpsServer.EMPTY_PAGE = `https://localhost:${httpsPort}/empty.html`;
+  state.httpsServer.EMPTY_PAGE2 = `https://localhost:${httpsPort}/empty2.html`;
+});
+
+testRunner.afterAll(async({server, httpsServer}) => {
+  await Promise.all([
+    server.stop(),
+    httpsServer.stop(),
+  ]);
+});
+
+testRunner.beforeEach(async({server, httpsServer}) => {
+  server.reset();
+  httpsServer.reset();
+});
+
+const product = process.env['PRODUCT'];
+const pptrFirefox = require('..');
+const pptrChromium = require('puppeteer');
+if (product) {
+  console.log(`WARNING: Running with ${product} only product because of PRODUCT env`);
+  require('./puppeteer.spec.js').addTests({testRunner, product, puppeteer: product === 'chromium' ? pptrChromium : pptrFirefox});
+} else {
+  require('./puppeteer.spec.js').addTests({testRunner, product: 'chromium', puppeteer: pptrChromium});
+  require('./puppeteer.spec.js').addTests({testRunner, product: 'firefox', puppeteer: pptrFirefox});
+}
+
+if (process.env.CI && testRunner.hasFocusedTestsOrSuites()) {
+  console.error('ERROR: "focused" tests/suites are prohibitted on bots. Remove any "fit"/"fdescribe" declarations.');
+  process.exit(1);
+}
+
+new Reporter(testRunner, path.join(__dirname, '..'));
+testRunner.run();