Use Zone to correctly measure async operations.

pkg/compiler/lib/src/dump_info.dart

 // Copyright (c) 2013, 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 dump_info;
 
 import 'dart:convert'
     show ChunkedConversionSink, JsonEncoder, StringConversionSink;
 
 import 'package:dart2js_info/info.dart';
@@ skipping 561 matching lines @@
     }
 
     result.deferredFiles = compiler.deferredLoadTask.computeDeferredMap();
     stopwatch.stop();
     result.program = new ProgramInfo(
         entrypoint: infoCollector._elementToInfo[compiler.mainFunction],
         size: _programSize,
         dart2jsVersion:
             compiler.options.hasBuildId ? compiler.options.buildId : null,
         compilationMoment: new DateTime.now(),
-        compilationDuration: compiler.totalCompileTime.elapsed,
+        compilationDuration: compiler.measurer.wallClock.elapsed,
         toJsonDuration: stopwatch.elapsedMilliseconds,
         dumpInfoDuration: this.timing,
         noSuchMethodEnabled: compiler.backend.enabledNoSuchMethod,
         minified: compiler.options.enableMinification);
 
     ChunkedConversionSink<Object> sink = encoder.startChunkedConversion(
         new StringConversionSink.fromStringSink(buffer));
     sink.add(new AllInfoJsonCodec().encode(result));
     reporter.reportInfo(NO_LOCATION_SPANNABLE, MessageKind.GENERIC, {
       'text': "View the dumped .info.json file at "
           "https://dart-lang.github.io/dump-info-visualizer"
     });
   }
 }