Add more info if create_new_folder.js test fails

In case of failure, debug/report the folder name in the log.

Test: browser_tests --gtest_filter="CreateNewFolder/FilesApp*"
Bug: 876267
Change-Id: I1341c3f746506521a172829fdcf121cbe2030920
Reviewed-on: https://chromium-review.googlesource.com/1207787
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590215}

ui/file_manager/integration_tests/file_manager/create_new_folder.js

@@ -127,7 +127,9 @@ function createNewFolder(appId, initialEntrySet, selector) {
   }).then(function(elements) {
     // Check: the test folder only should be 'selected'.
     chrome.test.assertEq(1, elements.length);
-    chrome.test.assertEq(0, elements[0].text.indexOf('Test Folder Name--'));
+    chrome.test.assertEq(
+        0, elements[0].text.indexOf('Test Folder Name--'),
+        'Actual text was: ' + elements[0].text);
   });
 }