Fixes no rel noopener when properties of anchor element cannot be resolved anymore (#1818)

* Fixes no rel noopener when anchor element is not available anymore. #1802
* Change rellnoopener to getAttribute('href')

lighthouse-cli/test/smokehouse/dobetterweb/dbw-expectations.js

@@ -39,9 +39,11 @@ module.exports = [
       },
       'external-anchors-use-rel-noopener': {
         score: false,
+        debugString: 'Lighthouse was unable to determine the destination of some anchor tags. ' +
+                     'If they are not used as hyperlinks, consider removing the _blank target.',
         extendedInfo: {
           value: {
-            length: 2
+            length: 3
           }
         }
       },

lighthouse-core/gather/driver.js

@@ -494,7 +494,7 @@ class Driver {
   * @return {!Promise<string>} The property value, or null, if property not found
   */
   getObjectProperty(objectId, propName) {
-    return new Promise((resolve, reject) => {
+    return new Promise(resolve => {
       this.sendCommand('Runtime.getProperties', {
         objectId,
         accessorPropertiesOnly: true,
@@ -508,7 +508,7 @@ class Driver {
         if (propertyForName) {
           resolve(propertyForName.value.value);
         } else {
-          reject(null);
+          resolve(null);
         }
       });
     });

lighthouse-core/gather/gatherers/dobetterweb/anchors-with-no-rel-noopener.js

@@ -29,7 +29,7 @@ class AnchorsWithNoRelNoopener extends Gatherer {
       .then(failingNodeList => {
         const failingNodes = failingNodeList.map(node => {
           return Promise.all([
-            node.getProperty('href'),
+            node.getAttribute('href'),
             node.getAttribute('rel'),
             node.getAttribute('target')
           ]);

lighthouse-core/lib/element.js

@@ -43,6 +43,7 @@ class Element {
         if (attrIndex === -1) {
           return null;
         }
+
         return resp.attributes[attrIndex + 1];
       });
   }