Telemetry: Initialize smoothness and thread_times metrics before page load, not after.

tools/perf/measurements/timeline_controller.py

Index: tools/perf/measurements/timeline_controller.py
diff --git a/tools/perf/measurements/timeline_controller.py b/tools/perf/measurements/timeline_controller.py
index 77d39341e871ffcfb19080634eb1a2265a9c53eb..4cd0008b27de9fea89ba7ebe66f8e1593da1855e 100644
--- a/tools/perf/measurements/timeline_controller.py
+++ b/tools/perf/measurements/timeline_controller.py
@@ -21,7 +21,7 @@ class TimelineController(object):
     self._smooth_records = []
     self._interaction = None
 
-  def Start(self, page, tab):
+  def SetUp(self, page, tab):
     """Starts gathering timeline data.
 
     """
@@ -36,6 +36,8 @@ class TimelineController(object):
     else:
       categories = page.GetSyntheticDelayCategories()
     tab.browser.StartTracing(','.join(categories))
+
+  def Start(self, tab):
     # Start the smooth marker for all actions.
     runner = action_runner.ActionRunner(tab)
     self._interaction = runner.BeginInteraction(