Merge all logic in PageMeasurementResults to PageTestResults.

tools/telemetry/telemetry/web_perf/metrics/fast_metric_unittest.py

Index: tools/telemetry/telemetry/web_perf/metrics/fast_metric_unittest.py
diff --git a/tools/telemetry/telemetry/web_perf/metrics/fast_metric_unittest.py b/tools/telemetry/telemetry/web_perf/metrics/fast_metric_unittest.py
index 4fea0b853c45cf0ca6044bfe343ebac0cfa9a250..edb64bc1ba02906558e8308b6f26ac6ed3d9fcb3 100644
--- a/tools/telemetry/telemetry/web_perf/metrics/fast_metric_unittest.py
+++ b/tools/telemetry/telemetry/web_perf/metrics/fast_metric_unittest.py
@@ -42,9 +42,10 @@ class RendererThreadHelper(object):
         for s in self._async_slices]
     results = page_measurement_results.PageMeasurementResults()
     fake_page = None
-    results.WillMeasurePage(fake_page)
+    results.StartTest(fake_page)
     metric.AddResults(self._model, self._renderer_thread, interaction_records,
                       results)
+    results.StopTest(fake_page)
     return results