Reland: Network Service: Use histograms instead of chartjsons for network service performance tests

The initial upload of this CL is the same as:
https://chromium-review.googlesource.com/c/chromium/src/+/1454633

New changes in the CL from the above original CL:
Modifies the output histogram filename to be "histograms.json"

This CL modifies the network service performance tests to generate
histograms instead of chartjsons so that the Pinpoint can automatic
bisect CLs.

TBR=crouleau@chromium.org, jam@chromium.org, simonhatch@chromium.org, benjhayden@chromium.org

Bug: 927155
Change-Id: I7b9dcd9fdabe7b5e59d7d5143b1ec1e2ffd9606e
Reviewed-on: https://chromium-review.googlesource.com/c/1456694Reviewed-by: Jun Cai <juncai@chromium.org>
Reviewed-by: Simon Hatch <simonhatch@chromium.org>
Commit-Queue: Jun Cai <juncai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629755}

testing/buildbot/chromium.perf.fyi.json

@@ -272,7 +272,7 @@
           "--benchmarks=loading.desktop.network_service",
           "-v",
           "--upload-results",
-          "--output-format=chartjson",
+          "--output-format=histograms",
           "--browser=release"
         ],
         "isolate_name": "performance_test_suite",

tools/perf/contrib/network_service/loading.py

@@ -15,6 +15,8 @@ from telemetry.internal import story_runner
 from telemetry.value import none_values
 from telemetry.value.list_of_scalar_values import StandardDeviation
 
+from tracing.value import convert_chart_json
+
 def _ListSubtraction(diff_list, control_list):
   """Subtract |control_list|'s elements from the corresponding elements in
   |diff_list|, and store the results in |diff_list|.
@@ -157,10 +159,12 @@ class LoadingDesktopNetworkService(loading.LoadingDesktop):
   def Run(self, finder_options):
     """We shouldn't be overriding this according to
     telemetry.benchmark.Benchmark"""
-    assert 'chartjson' in finder_options.output_formats, (
-      'loading.desktop.network_service requires --output-format=chartjson. '
-      'Please contact owner to rewrite the benchmark if chartjson is going '
-      'away.')
+    assert 'histograms' in finder_options.output_formats, (
+      'loading.desktop.network_service requires --output-format=histograms.')
+
+    # feed the story_runner with 'chartjson' output formats.
+    finder_options.output_formats = ['chartjson']
+
     assert finder_options.output_dir
     output_dir = finder_options.output_dir
     temp_file_path = os.path.join(output_dir, 'results-chart.json')
@@ -198,6 +202,17 @@ class LoadingDesktopNetworkService(loading.LoadingDesktop):
       with open(temp_file_path, 'w') as f:
         json.dump(enabled_chart_json, f, indent=2, separators=(',', ': '))
         f.write('\n')
+      logging.info('Converting chartjsons to histograms')
+      histogram_result = convert_chart_json.ConvertChartJson(temp_file_path)
+      if histogram_result.returncode != 0:
+        logging.error('Error converting chart json to Histograms:\n' +
+            histogram_result.stdout)
+        return 1
+
+      temp_file_path = os.path.join(output_dir, 'histograms.json')
+      with open(temp_file_path, 'w') as f:
+        f.write(histogram_result.stdout)
+
     return 0
 
   def SetExtraBrowserOptions(self, options):