Enable disabling network throttling.

Due to some oddness of how chrome handles h2 and h2 push when network
throttling is enabled, it is useful to be able to disable this.

To accomplish this goal, I added a new flag to the CLI, and then
modified the driver classes to take an options value and store it on the
class instance. The options are proxied down from the CLI flags ... into
the core lighthouse module and then directly into cri driver
constructor.

lighthouse-cli/bin.ts

@@ -62,7 +62,8 @@ const cli = yargs
     'list-all-audits',
     'list-trace-categories',
     'config-path',
-    'perf'
+    'perf',
+    'disable-network-throttling',
   ], 'Configuration:')
   .describe({
     'mobile': 'Emulates a Nexus 5X',
@@ -74,6 +75,7 @@ const cli = yargs
     'perf': 'Use a performance-test-only configuration',
     'skip-autolaunch': 'Skip autolaunch of chrome when accessing port 9222 fails',
     'select-chrome': 'Choose chrome location to use when multiple installations are found',
+    'disable-network-throttling': 'Disable network throttling when running audits.',
   })
 
   .group([
@@ -161,7 +163,7 @@ const cleanup = {
   }
 };
 
-function launchChromeAndRun(addresses) {
+function launchChromeAndRun(addresses: Array<string>) {
   const launcher = new ChromeLauncher({
     autoSelectChrome: !cli.selectChrome,
   });

lighthouse-core/gather/drivers/cri.js

@@ -23,8 +23,8 @@ const port = process.env.PORT || 9222;
 const log = require('../../lib/log.js');
 
 class CriDriver extends Driver {
-  constructor() {
-    super();
+  constructor(opts) {
+    super(opts);
 
     /**
      * Chrome remote interface instance.

lighthouse-core/gather/drivers/driver.js

@@ -28,10 +28,15 @@ const PAUSE_AFTER_LOAD = 500;
 
 class Driver {
 
-  constructor() {
+  constructor(opts) {
+    opts = opts || {};
+
+    this.disableNetworkThrottling = opts._disableNetworkThrottling || false;
+
     this._traceEvents = [];
     this._traceCategories = Driver.traceCategories;
     this._eventEmitter = null;
+    this.opts = opts;
   }
 
   static get traceCategories() {
@@ -492,7 +497,13 @@ class Driver {
   beginEmulation() {
     return Promise.all([
       emulation.enableNexus5X(this),
-      emulation.enableNetworkThrottling(this)
+      () => {
+        if (this.opts['disable-network-throttling']) {
+          return Promise.resolve();
+        }
+
+        return emulation.enableNetworkThrottling();
+      }
     ]);
   }
 
@@ -512,7 +523,7 @@ class Driver {
    */
   goOnline(options) {
     return this.sendCommand('Network.enable').then(_ => {
-      if (options.flags.mobile) {
+      if (options.flags.mobile && !this.opts['disable-network-throttling']) {
         return emulation.enableNetworkThrottling(this);
       }
 

lighthouse-core/gather/drivers/extension.js

@@ -24,8 +24,8 @@ const EventEmitter = require('events').EventEmitter;
 
 class ExtensionDriver extends Driver {
 
-  constructor() {
-    super();
+  constructor(opts) {
+    super(opts);
     this._tabId = null;
 
     this._eventEmitter = new EventEmitter();

lighthouse-core/index.js

@@ -58,7 +58,7 @@ module.exports = function(url, flags, configJSON) {
     // Use ConfigParser to generate a valid config file
     const config = new Config(configJSON, flags.configPath);
 
-    const driver = new ChromeProtocol();
+    const driver = new ChromeProtocol(flags);
 
     // kick off a lighthouse run
     resolve(Runner.run(driver, {url, flags, config}));