Create classes_util API, change discover to return a list instead of a dict.

tools/telemetry/telemetry/testing/story_set_smoke_test.py

Index: tools/telemetry/telemetry/testing/story_set_smoke_test.py
diff --git a/tools/telemetry/telemetry/testing/story_set_smoke_test.py b/tools/telemetry/telemetry/testing/story_set_smoke_test.py
index 008773f5f7eaf8c4b0848cb0651ecded627abdcb..d0a8d575bf6eb2dba1bba0d4ed26bf68420ad43d 100644
--- a/tools/telemetry/telemetry/testing/story_set_smoke_test.py
+++ b/tools/telemetry/telemetry/testing/story_set_smoke_test.py
@@ -6,10 +6,10 @@ import logging
 import os
 import unittest
 
-from telemetry.core import discover
 from telemetry.internal.browser import browser_credentials
 from telemetry import page
 from telemetry import story as story_module
+from telemetry.util import classes_util
 from telemetry.wpr import archive_info
 
 
@@ -23,9 +23,9 @@ class StorySetSmokeTest(unittest.TestCase):
   def GetAllStorySetClasses(self, story_sets_dir, top_level_dir):
     # We can't test page sets that aren't directly constructable since we
     # don't know what arguments to put for the constructor.
-    return discover.DiscoverClasses(story_sets_dir, top_level_dir,
-                                    story_module.StorySet,
-                                    directly_constructable=True).values()
+    return classes_util.DiscoverClasses(story_sets_dir, top_level_dir,
+                                        story_module.StorySet,
+                                        directly_constructable=True)
 
   def CheckArchive(self, story_set):
     """Verify that all URLs of pages in story_set have an associated archive."""