Deserialize ResolvedAsts and ResolutionImpacts only when needed for compilation.

tests/compiler/dart2js/serialization/helper.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 dart2js.serialization_helper;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:compiler/src/commandline_options.dart';
@@ skipping 131 matching lines @@
 class SerializationResult {
   final Compiler compiler;
   final SerializedData serializedData;
 
   SerializationResult(this.compiler, this.serializedData);
 }
 
 Future<SerializationResult> serialize(Uri entryPoint,
     {Map<String, String> memorySourceFiles: const <String, String>{},
      List<Uri> resolutionInputs: const <Uri>[],
-     Uri dataUri}) async {
+     Uri dataUri,
+     bool deserializeCompilationDataForTesting: false}) async {
   if (dataUri == null) {
     dataUri = Uri.parse('memory:${DEFAULT_DATA_FILE_NAME}');
   }
   OutputCollector outputCollector = new OutputCollector();
   Compiler compiler = compilerFor(
       options: [Flags.resolveOnly],
       memorySourceFiles: memorySourceFiles,
       resolutionInputs: resolutionInputs,
       outputProvider: outputCollector);
+  compiler.serialization.deserializeCompilationDataForTesting =
+      deserializeCompilationDataForTesting;
   await compiler.run(entryPoint);
   SerializedData serializedData = new SerializedData(
       dataUri, outputCollector.getOutput('', 'data'));
   return new SerializationResult(compiler, serializedData);
 }
 
 class SerializedData {
   final Uri uri;
   final String data;
 
@@ skipping 113 matching lines @@
   print('$taskTitle: $title');
   print('----------------------------------------------------------------');
   var result = await task();
   stopwatch.stop();
   int elapsedMilliseconds = stopwatch.elapsedMilliseconds;
   print('$taskTitle: $title: ${elapsedMilliseconds}ms');
   measurementResults.add(
       new MeasurementResult(title, taskTitle, elapsedMilliseconds));
   return result;
 }