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/index.js

@@ -0,0 +1,56 @@
+/**
+ * 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 FirefoxLauncher = require('./lib/firefox/Launcher.js').Launcher;
+const BrowserFetcher = require('./lib/firefox/BrowserFetcher.js');
+
+class Puppeteer {
+  constructor() {
+    this._firefoxLauncher = new FirefoxLauncher();
+  }
+
+  async launch(options = {}) {
+    const {
+      args = [],
+      dumpio = !!process.env.DUMPIO,
+      handleSIGHUP = true,
+      handleSIGINT = true,
+      handleSIGTERM = true,
+      headless = (process.env.HEADLESS || 'true').trim().toLowerCase() === 'true',
+      defaultViewport = {width: 800, height: 600},
+      ignoreHTTPSErrors = false,
+      slowMo = 0,
+      executablePath = this.executablePath(),
+    } = options;
+    options = {
+      args, slowMo, dumpio, executablePath, handleSIGHUP, handleSIGINT, handleSIGTERM, headless, defaultViewport,
+      ignoreHTTPSErrors
+    };
+    return await this._firefoxLauncher.launch(options);
+  }
+
+  createBrowserFetcher(options) {
+    return new BrowserFetcher(__dirname, options);
+  }
+
+  executablePath() {
+    const browserFetcher = new BrowserFetcher(__dirname, { product: 'firefox' });
+    const revision = require('./package.json').puppeteer.firefox_revision;
+    const revisionInfo = browserFetcher.revisionInfo(revision);
+    return revisionInfo.executablePath;
+  }
+}
+
+module.exports = new Puppeteer();