Node 6 support (#484)

This patch:
- introduces a transpiler which substitutes async/await logic with
generators.
- starts using the transpiler to generate a node6-compatible version of puppeteer
- introduces a runtime-check to decide which version of code to use

Fixes #316.

utils/node6-transform/test/test.js

@@ -0,0 +1,67 @@
+/**
+ * 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.
+ */
+const transformAsyncFunctions = require('../TransformAsyncFunctions');
+
+describe('TransformAsyncFunctions', function() {
+  it('should convert a function expression', function(done) {
+    const input = `(async function(){ return 123 })()`;
+    const output = eval(transformAsyncFunctions(input));
+    expect(output instanceof Promise).toBe(true);
+    output.then(result => expect(result).toBe(123)).then(done);
+  });
+  it('should convert an arrow function', function(done) {
+    const input = `(async () => 123)()`;
+    const output = eval(transformAsyncFunctions(input));
+    expect(output instanceof Promise).toBe(true);
+    output.then(result => expect(result).toBe(123)).then(done);
+  });
+  it('should convert an arrow function with curly braces', function(done) {
+    const input = `(async () => { return 123 })()`;
+    const output = eval(transformAsyncFunctions(input));
+    expect(output instanceof Promise).toBe(true);
+    output.then(result => expect(result).toBe(123)).then(done);
+  });
+  it('should convert a function declaration', function(done) {
+    const input = `async function f(){ return 123; } f();`;
+    const output = eval(transformAsyncFunctions(input));
+    expect(output instanceof Promise).toBe(true);
+    output.then(result => expect(result).toBe(123)).then(done);
+  });
+  it('should convert await', function(done) {
+    const input = `async function f(){ return 23 + await Promise.resolve(100); } f();`;
+    const output = eval(transformAsyncFunctions(input));
+    expect(output instanceof Promise).toBe(true);
+    output.then(result => expect(result).toBe(123)).then(done);
+  });
+  it('should convert method', function(done) {
+    const input = `class X{async f() { return 123 }} (new X()).f();`;
+    const output = eval(transformAsyncFunctions(input));
+    expect(output instanceof Promise).toBe(true);
+    output.then(result => expect(result).toBe(123)).then(done);
+  });
+  it('should pass arguments', function(done) {
+    const input = `(async function(a, b){ return await a + await b })(Promise.resolve(100), 23)`;
+    const output = eval(transformAsyncFunctions(input));
+    expect(output instanceof Promise).toBe(true);
+    output.then(result => expect(result).toBe(123)).then(done);
+  });
+  it('should still work across eval', function(done) {
+    const input = `var str = (async function(){ return 123; }).toString(); eval('(' + str + ')')();`;
+    const output = eval(transformAsyncFunctions(input));
+    expect(output instanceof Promise).toBe(true);
+    output.then(result => expect(result).toBe(123)).then(done);
+  });
+});