Add pdf.js example (puppeteer#216)

add pdf.js example

examples/.eslintrc.js

@@ -0,0 +1,15 @@
+module.exports = {
+    "extends": "../.eslintrc.js",
+    /**
+     * ESLint rules
+     *
+     * All available rules: http://eslint.org/docs/rules/
+     *
+     * Rules take the following form:
+     *   "rule-name", [severity, { opts }]
+     * Severity: 2 == error, 1 == warning, 0 == off.
+     */
+    "rules": {
+        "indent": [2, 2, { "SwitchCase": 1, "CallExpression": {"arguments": 2}, "MemberExpression": 2, "outerIIFEBody": 0 }],
+    }
+};

examples/pdf.js

@@ -0,0 +1,33 @@
+/**
+ * Copyright 2017 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.
+ */
+
+(async() => {
+
+const {Browser} = require('puppeteer');
+const browser = new Browser();
+
+const page = await browser.newPage();
+await page.navigate('https://news.ycombinator.com', {waitUntil: 'networkidle'});
+// page.pdf() is currently supported only in headless mode.
+// @see https://bugs.chromium.org/p/chromium/issues/detail?id=753118
+await page.pdf({
+  path: 'hn.pdf',
+  format: 'A4'
+});
+
+browser.close();
+
+})();