cleanup and improve A/B fasta test harness

pkg/front_end/lib/src/fasta/outline.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.outline;
 
 import 'dart:async' show Future;
 
+import 'dart:convert' show JSON;
+
 import 'dart:io' show exitCode;
 
 import 'kernel/verifier.dart' show verifyProgram;
 
 import 'compiler_command_line.dart' show CompilerCommandLine;
 
 import 'compiler_context.dart' show CompilerContext;
 
 import 'errors.dart' show InputError, inputError;
 
 import 'kernel/kernel_target.dart' show KernelTarget;
 
 import 'dill/dill_target.dart' show DillTarget;
 
 import 'ticker.dart' show Ticker;
 
 import 'translate_uri.dart' show TranslateUri;
 
+const bool summary = const bool.fromEnvironment("summary", defaultValue: false);
 const int iterations = const int.fromEnvironment("iterations", defaultValue: 1);
 
 compileEntryPoint(List<String> arguments) async {
+  // Timing results for each iteration
+  List<double> elapsedTimes = <double>[];
+
   for (int i = 0; i < iterations; i++) {
     if (i > 0) {
-      print("\n");
+      print("\n\n=== Iteration ${i+1} of $iterations");
     }
+    var stopwatch = new Stopwatch()..start();
     await compile(arguments);
+    stopwatch.stop();
+
+    elapsedTimes.add(stopwatch.elapsedMilliseconds.toDouble());
+  }
+
+  if (summary) {
+    var json = JSON.encode(<String, dynamic>{'elapsedTimes': elapsedTimes});
+    print('\nSummary: $json');
   }
 }
 
 outlineEntryPoint(List<String> arguments) async {
   for (int i = 0; i < iterations; i++) {
     if (i > 0) {
       print("\n");
     }
     await outline(arguments);
   }
@@ skipping 88 matching lines @@
         exitCode = 1;
         print("Verification of program failed: $e");
         if (s != null && c.options.verbose) {
           print(s);
         }
       }
     }
     return uri;
   }
 }