wpt_common.py: Add artifacts path to JSON results

For blink web tests, resultsdb requires the artifact paths to be in
lists.

Bug: 937369
Change-Id: I1a33fa340778129c9b4f7ed8c834cfa22a728f59
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2247082Reviewed-by: Luke Z <lpz@chromium.org>
Commit-Queue: Rakib Hasan <rmhasan@google.com>
Cr-Commit-Position: refs/heads/master@{#779584}

testing/scripts/wpt_common.py

@@ -98,11 +98,9 @@ class BaseWptScriptAdapter(common.BaseIsolatedScriptArgsAdapter):
                 return
             log_artifact = root_node["artifacts"].pop("log", None)
             if log_artifact:
-                self._write_log_artifact(results_dir, path_so_far, log_artifact)
-                # TODO(lpz): Adding the "actual_text" artifact below breaks the
-                # results viewer link on the builder. Investigate why.
-                # Add the path for the artifact file to the json output.
-                # root_node["artifacts"]["actual_text"] = artifact_subpath
+                artifact_subpath = self._write_log_artifact(
+                    results_dir, path_so_far, log_artifact)
+                root_node["artifacts"]["actual_text"] = [artifact_subpath]
 
             # TODO(lpz): For now we just discard the screenshot artifact to keep
             # the output file size small. Writing screenshots to disk will be