Introduce OutputFormatter interface and wire it through PageTestResults.

tools/telemetry/telemetry/results/csv_output_formatter.py

Index: tools/telemetry/telemetry/results/csv_output_formatter.py
diff --git a/tools/telemetry/telemetry/results/csv_page_measurement_results.py b/tools/telemetry/telemetry/results/csv_output_formatter.py
similarity index 51%
rename from tools/telemetry/telemetry/results/csv_page_measurement_results.py
rename to tools/telemetry/telemetry/results/csv_output_formatter.py
index 8d396354423704e09df5d9fdbac4db241c5e6c66..3c10657adc4d7599eeeb0e046d5f2e93764e2e38 100644
--- a/tools/telemetry/telemetry/results/csv_page_measurement_results.py
+++ b/tools/telemetry/telemetry/results/csv_output_formatter.py
@@ -4,30 +4,27 @@
 
 import csv
 
-from telemetry.results import page_measurement_results
+from telemetry.results import output_formatter
 from telemetry.value import merge_values
 
 
-class CsvPageMeasurementResults(
-    page_measurement_results.PageMeasurementResults):
+class CsvOutputFormatter(output_formatter.OutputFormatter):
   def __init__(self, output_stream):
-    super(CsvPageMeasurementResults, self).__init__(output_stream)
-    self._results_writer = csv.writer(self._output_stream)
-    self._representative_value_names = None
+    super(CsvOutputFormatter, self).__init__(output_stream)
 
-  def PrintSummary(self):
-    try:
-      values = merge_values.MergeLikeValuesFromSamePage(
-          self.all_page_specific_values)
-      self._OutputHeader(values)
-      value_groups_by_page = merge_values.GroupStably(
-          values, lambda value: value.page.url)
-      for values_for_page in value_groups_by_page:
-        self._OutputValuesForPage(values_for_page[0].page, values_for_page)
-    finally:
-      super(CsvPageMeasurementResults, self).PrintSummary()
+  def Format(self, page_test_results):
+    values = merge_values.MergeLikeValuesFromSamePage(
+        page_test_results.all_page_specific_values)
+    writer = csv.writer(self.output_stream)
+    header_value_names = self._OutputHeader(values, writer)
+    value_groups_by_page = merge_values.GroupStably(
+        values, lambda value: value.page.url)
+    for values_for_page in value_groups_by_page:
+      self._OutputValuesForPage(
+          header_value_names, values_for_page[0].page, values_for_page,
+          writer)
 
-  def _OutputHeader(self, values):
+  def _OutputHeader(self, values, csv_writer):
     """Output the header rows.
 
     This will retrieve the header string from the given values. As a
@@ -39,33 +36,39 @@ class CsvPageMeasurementResults(
     Args:
       values: A set of values from which to extract the header string,
           which is the value name and the units.
+      writer: A csv.writer instance.
+
+    Returns:
+      The value names being output on the header, in the order of
+      output.
     """
     representative_values = {}
     for value in values:
       if value.name not in representative_values:
         representative_values[value.name] = value
-    self._representative_value_names = list(
-        representative_values.keys())
-    self._representative_value_names.sort()
+    header_value_names = list(representative_values.keys())
+    header_value_names.sort()
 
     row = ['page_name']
-    for value_name in self._representative_value_names:
+    for value_name in header_value_names:
       units = representative_values[value_name].units
       row.append('%s (%s)' % (value_name, units))
-    self._results_writer.writerow(row)
-    self._output_stream.flush()
+    csv_writer.writerow(row)
+    self.output_stream.flush()
+    return header_value_names
 
-  def _OutputValuesForPage(self, page, page_values):
+  def _OutputValuesForPage(self, header_value_names, page, page_values,
+                           csv_writer):
     row = [page.display_name]
     values_by_value_name = {}
     for value in page_values:
       values_by_value_name[value.name] = value
 
-    for value_name in self._representative_value_names:
+    for value_name in header_value_names:
       value = values_by_value_name.get(value_name, None)
       if value and value.GetRepresentativeNumber():
         row.append('%s' % value.GetRepresentativeNumber())
       else:
         row.append('-')
-    self._results_writer.writerow(row)
-    self._output_stream.flush()
+    csv_writer.writerow(row)
+    self.output_stream.flush()