htmlTag was missing from the list of stringAttributes for an automationNode

BUG=718448

Review-Url: https://codereview.chromium.org/2857413002
Cr-Commit-Position: refs/heads/master@{#469501}

chrome/renderer/resources/extensions/automation/automation_node.js

@@ -704,6 +704,7 @@ var stringAttributes = [
     'containerLiveStatus',
     'description',
     'display',
+    'htmlTag',
     'imageDataUrl',
     'language',
     'liveRelevant',

chrome/test/data/extensions/api_test/automation/sites/attributes.html

@@ -76,5 +76,9 @@
   <div id="check-test-2" aria-label="check-test-2" role="checkbox" aria-checked="false">Unchecked</div>
   <div id="check-test-3" aria-label="check-test-3" role="checkbox" aria-checked="mixed">Mixed</div>
   <div id="check-test-4" aria-label="check-test-4" aria-checked="true">Not a checkbox</div>
+
+  <!-- htmlTag attribute -->
+  <figure>Go figure!</figure>
+
 </body>
 </html>

chrome/test/data/extensions/api_test/automation/tests/tabs/attributes.js

@@ -300,6 +300,14 @@ var allTests = [
 
     chrome.test.succeed();
   },
+
+  function testHtmlTagAttribute() {
+    var figure = rootNode.find({ attributes: { htmlTag: 'figure' } });
+    assertTrue(Boolean(figure));
+    assertEq(figure.htmlTag, 'figure');
+
+    chrome.test.succeed();
+  }
 ];
 
 setUpAndRunTests(allTests, 'attributes.html');