Outputing comma-separated report with percentages

tools/testing/dart/test_progress.dart

Index: tools/testing/dart/test_progress.dart
diff --git a/tools/testing/dart/test_progress.dart b/tools/testing/dart/test_progress.dart
index bb31d29f6922a3ecf3b37fb303bb8f945c9f42aa..e93a888e3dc479eb304e35ad24fb639178d173d3 100644
--- a/tools/testing/dart/test_progress.dart
+++ b/tools/testing/dart/test_progress.dart
@@ -10,6 +10,7 @@ import "dart:io" as io;
 import "dart:convert" show JSON;
 import "path.dart";
 import "status_file_parser.dart";
+import "summary_report.dart";
 import "test_runner.dart";
 import "test_suite.dart";
 import "utils.dart";
@@ -307,9 +308,16 @@ class UnexpectedCrashDumpArchiver extends EventListener {
 
 
 class SummaryPrinter extends EventListener {
+  final bool jsonOnly;
+
+  SummaryPrinter({this.jsonOnly});
+
   void allTestsKnown() {
-    if (SummaryReport.total > 0) {
-      SummaryReport.printReport();
+    if (jsonOnly) {
+      print("JSON:");
+      print(JSON.encode(summaryReport.values));
+    } else {
+      summaryReport.printReport();
     }
   }
 }