Outputing json test results to output.json

BUG=chromium:717394

Review-Url: https://codereview.chromium.org/2979703002
Cr-Commit-Position: refs/heads/master@{#485984}

testing/scripts/run_telemetry_benchmark_as_googletest.py

@@ -66,6 +66,8 @@ def main():
     failures = []
     chartjson_results_present = '--output-format=chartjson' in rest_args
     chartresults = None
+    json_test_results_present = '--output-format=json-test-results' in rest_args
+    json_test_results = None
 
     results = None
     try:
@@ -97,6 +99,11 @@ def main():
             failures.append(name)
         valid = bool(rc == 0 or failures)
 
+      if json_test_results_present:
+        tempfile_name = os.path.join(tempfile_dir, 'test-results.json')
+        with open(tempfile_name) as f:
+          json_test_results = json.load(f)
+
     except Exception:
       traceback.print_exc()
       if results:
@@ -116,10 +123,13 @@ def main():
         open(args.isolated_script_test_chartjson_output, 'w')
       json.dump(chartresults, chartjson_output_file)
 
-    json.dump({
-        'valid': valid,
-        'failures': failures
-    }, args.isolated_script_test_output)
+    if not json_test_results_present:
+      json_test_results = {
+          'valid': valid,
+          'failures': failures
+      }
+
+    json.dump(json_test_results, args.isolated_script_test_output)
     return rc
 
   finally: