Refactor the way page_set is checked in test_runner and record_wprd

tools/telemetry/telemetry/test_runner.py

Index: tools/telemetry/telemetry/test_runner.py
diff --git a/tools/telemetry/telemetry/test_runner.py b/tools/telemetry/telemetry/test_runner.py
index 227aa201680573dc42c31780c567ff66500cef4f..66b923bb192c7c266f4bd16df4a880e92b9e110f 100644
--- a/tools/telemetry/telemetry/test_runner.py
+++ b/tools/telemetry/telemetry/test_runner.py
@@ -138,8 +138,8 @@ class Run(command_line.OptparseCommand):
       if not os.path.exists(page_set_path):
         parser.error('Page set not found.')
       if not (os.path.isfile(page_set_path) and
-              os.path.splitext(page_set_path)[1] == '.json'):
-        parser.error('Page set is not a JSON file.')
+              discover.IsPageSetFile(page_set_path)):
+        parser.error('Unsupported page set file format.')
 
       class TestWrapper(test.Test):
         test = test_class