[telemetry] Add TraceResult as return value from tracing, and placeholder trace_event_importer.

tools/telemetry/telemetry/run_tests.py

Index: tools/telemetry/telemetry/run_tests.py
diff --git a/tools/telemetry/telemetry/run_tests.py b/tools/telemetry/telemetry/run_tests.py
index 4e79815c2a524f644b91298880e3227c6818babd..2c857df71af49b9bbd61774be8fd43066788e3de 100644
--- a/tools/telemetry/telemetry/run_tests.py
+++ b/tools/telemetry/telemetry/run_tests.py
@@ -17,12 +17,6 @@ def RequiresBrowserOfType(*types):
   return wrap
 
 def Discover(start_dir, pattern = 'test*.py', top_level_dir = None):
-  if hasattr(unittest.defaultTestLoader, 'discover'):
-    return unittest.defaultTestLoader.discover( # pylint: disable=E1101
-      start_dir,
-      pattern,
-      top_level_dir)
-
   modules = []
   for dirpath, _, filenames in os.walk(start_dir):
     for filename in filenames: