add goOffline/goOnline methods to driver

lighthouse-core/gather/drivers/driver.js

@@ -381,6 +381,30 @@ class Driver {
     ]);
   }
 
+  /**
+   * Emulate internet disconnection.
+   * @return {!Promise}
+   */
+  goOffline() {
+    return this.sendCommand('Network.enable').then(_ => emulation.goOffline(this));
+  }
+
+  /**
+   * Enable internet connection, using emulated mobile settings if
+   * `options.flags.mobile` is true.
+   * @param {!Object} options
+   * @return {!Promise}
+   */
+  goOnline(options) {
+    return this.sendCommand('Network.enable').then(_ => {
+      if (options.flags.mobile) {
+        return emulation.enableNetworkThrottling(this);
+      }
+
+      return emulation.disableNetworkThrottling(this);
+    });
+  }
+
   cleanAndDisableBrowserCaches() {
     return Promise.all([
       this.clearBrowserCache(),

lighthouse-core/gather/gatherers/offline.js

@@ -19,30 +19,8 @@
 const Gatherer = require('./gatherer');
 
 class Offline extends Gatherer {
-
-  static config(opts) {
-    return {
-      offline: opts.offline,
-      // values of 0 remove any active throttling. crbug.com/456324#c9
-      latency: 0,
-      downloadThroughput: 0,
-      uploadThroughput: 0
-    };
-  }
-
-  static goOffline(driver) {
-    // Network.enable must be called for Network.emulateNetworkConditions to work
-    return driver.sendCommand('Network.enable').then(_ => {
-      driver.sendCommand('Network.emulateNetworkConditions', Offline.config({offline: true}));
-    });
-  }
-
-  static goOnline(driver) {
-    return driver.sendCommand('Network.emulateNetworkConditions', Offline.config({offline: false}));
-  }
-
   beforePass(options) {
-    return Offline.goOffline(options.driver);
+    return options.driver.goOffline();
   }
 
   afterPass(options, tracingData) {
@@ -55,7 +33,7 @@ class Offline extends Gatherer {
 
     this.artifact = navigationRecord ? navigationRecord.statusCode : -1;
 
-    return Offline.goOnline(options.driver);
+    return options.driver.goOnline(options);
   }
 }
 

lighthouse-core/lib/emulation.js

@@ -48,6 +48,21 @@ const TYPICAL_MOBILE_THROTTLING_METRICS = {
   offline: false
 };
 
+const OFFLINE_METRICS = {
+  offline: true,
+  // values of 0 remove any active throttling. crbug.com/456324#c9
+  latency: 0,
+  downloadThroughput: 0,
+  uploadThroughput: 0
+};
+
+const NO_THROTTLING_METRICS = {
+  latency: 0,
+  downloadThroughput: 0,
+  uploadThroughput: 0,
+  offline: false
+};
+
 function enableNexus5X(driver) {
   /**
    * Finalizes touch emulation by enabling `"ontouchstart" in window` feature detect
@@ -90,7 +105,17 @@ function enableNetworkThrottling(driver) {
   return driver.sendCommand('Network.emulateNetworkConditions', TYPICAL_MOBILE_THROTTLING_METRICS);
 }
 
+function disableNetworkThrottling(driver) {
+  return driver.sendCommand('Network.emulateNetworkConditions', NO_THROTTLING_METRICS);
+}
+
+function goOffline(driver) {
+  return driver.sendCommand('Network.emulateNetworkConditions', OFFLINE_METRICS);
+}
+
 module.exports = {
   enableNexus5X,
-  enableNetworkThrottling
+  enableNetworkThrottling,
+  disableNetworkThrottling,
+  goOffline
 };

lighthouse-core/test/gather/gatherers/offline-test.js

@@ -22,7 +22,10 @@ const assert = require('assert');
 const tracingData = require('../../fixtures/traces/network-records.json');
 
 const mockDriver = {
-  sendCommand() {
+  goOffline() {
+    return Promise.resolve();
+  },
+  goOnline() {
     return Promise.resolve();
   }
 };