Add trace events for some of telemetry internal functions

telemetry/telemetry/page/legacy_page_test.py

Index: telemetry/telemetry/page/legacy_page_test.py
diff --git a/telemetry/telemetry/page/legacy_page_test.py b/telemetry/telemetry/page/legacy_page_test.py
index 1c26c3658240b3fe5bd5890c9fea4af0599080b4..47b6f800b3ac6ab46a1f595a9173385e7738d0eb 100644
--- a/telemetry/telemetry/page/legacy_page_test.py
+++ b/telemetry/telemetry/page/legacy_page_test.py
@@ -4,6 +4,8 @@
 
 import logging
 
+from py_trace_event import trace_event
+
 from telemetry.core import exceptions
 from telemetry.internal.actions import action_runner as action_runner_module
 
@@ -53,6 +55,8 @@ class LegacyPageTest(object):
              page, 'body_children', 'count', body_child_count))
   """
 
+  __metaclass__ = trace_event.TracedMetaClass
+
   def __init__(self,
                needs_browser_restart_after_each_page=False,
                clear_cache_before_each_run=False):