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

tools/telemetry/telemetry/record_wpr.py

Index: tools/telemetry/telemetry/record_wpr.py
diff --git a/tools/telemetry/telemetry/record_wpr.py b/tools/telemetry/telemetry/record_wpr.py
index 9a668f997626b1f3eb1a936015a90561a5ae29cc..6f1d2bd193bd61e81fb538a2f83a450d853de989 100644
--- a/tools/telemetry/telemetry/record_wpr.py
+++ b/tools/telemetry/telemetry/record_wpr.py
@@ -8,13 +8,13 @@ import sys
 
 from telemetry import benchmark
 from telemetry import story
-from telemetry.core import discover
 from telemetry.core import util
 from telemetry.internal.browser import browser_options
 from telemetry.internal.results import results_options
 from telemetry.internal import story_runner
 from telemetry.internal.util import command_line
 from telemetry.page import page_test
+from telemetry.util import classes_util
 from telemetry.util import wpr_modes
 
 
@@ -71,15 +71,13 @@ def _GetSubclasses(base_dir, cls):
   Returns:
     dict of {underscored_class_name: benchmark class}
   """
-  return discover.DiscoverClasses(base_dir, base_dir, cls,
-                                  index_by_class_name=True)
+  return classes_util.DiscoverClassesByClassName(base_dir, base_dir, cls)
 
 
 def _MaybeGetInstanceOfClass(target, base_dir, cls):
   if isinstance(target, cls):
     return target
-  classes = _GetSubclasses(base_dir, cls)
-  return classes[target]() if target in classes else None
+  return classes_util.MaybeGetInstanceOfClass(target, base_dir, base_dir, cls)
 
 
 def _PrintAllImpl(all_items, item_name, output_stream):