Don't compute hashes in "--build-summary-exclude-informative" mode.

pkg/analyzer/lib/src/summary/summarize_elements.dart

 // Copyright (c) 2015, 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 serialization.elements;
 
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 119 matching lines @@
    * format that clients might need to be aware of (such as adding a kind of
    * data that was previously not summarized), this value should be incremented
    * by 1.
    */
   static const int currentMinorVersion = 0;
 
   final List<String> _linkedLibraryUris = <String>[];
   final List<LinkedLibraryBuilder> _linkedLibraries = <LinkedLibraryBuilder>[];
   final List<String> _unlinkedUnitUris = <String>[];
   final List<UnlinkedUnitBuilder> _unlinkedUnits = <UnlinkedUnitBuilder>[];
-  final List<String> _unlinkedUnitHashes = <String>[];
+  final List<String> _unlinkedUnitHashes;
+  final bool _excludeHashes;
+
+  /**
+   * Create a [PackageBundleAssembler].  If [excludeHashes] is `true`, hash
+   * computation will be skipped.
+   */
+  PackageBundleAssembler({bool excludeHashes: false})
+      : _excludeHashes = excludeHashes,
+        _unlinkedUnitHashes = excludeHashes ? null : <String>[];
 
   /**
    * Add a fallback library to the package bundle, corresponding to the library
    * whose defining compilation unit is located at [source].  Caller must also
    * call [addFallbackUnit] for all compilation units contained in the library
    * (including the defining compilation unit).
    */
   void addFallbackLibrary(Source source) {
     String uri = source.uri.toString();
     _linkedLibraryUris.add(uri);
@@ skipping 10 matching lines @@
     _unlinkedUnits.add(new UnlinkedUnitBuilder(
         fallbackModePath: path.relative(source.fullName)));
   }
 
   void addLinkedLibrary(String uri, LinkedLibraryBuilder library) {
     _linkedLibraries.add(library);
     _linkedLibraryUris.add(uri);
   }
 
   void addUnlinkedUnit(Source source, UnlinkedUnitBuilder unit) {
-    addUnlinkedUnitWithHash(source.uri.toString(), unit, _hash(source.contents.data));
+    addUnlinkedUnitWithHash(source.uri.toString(), unit,
+        _excludeHashes ? null : _hash(source.contents.data));
   }
 
-  void addUnlinkedUnitWithHash(String uri, UnlinkedUnitBuilder unit, String hash) {
+  void addUnlinkedUnitWithHash(
+      String uri, UnlinkedUnitBuilder unit, String hash) {
     _unlinkedUnitUris.add(uri);
     _unlinkedUnits.add(unit);
-    _unlinkedUnitHashes.add(hash);
+    _unlinkedUnitHashes?.add(hash);
   }
 
   /**
    * Assemble a new [PackageBundleBuilder] using the gathered information.
    */
   PackageBundleBuilder assemble() {
     return new PackageBundleBuilder(
         linkedLibraryUris: _linkedLibraryUris,
         linkedLibraries: _linkedLibraries,
         unlinkedUnitUris: _unlinkedUnitUris,
@@ skipping 1460 matching lines @@
       exportNames.add(new LinkedExportNameBuilder(
           name: name,
           dependency: serializeDependency(dependentLibrary),
           unit: unit,
           kind: kind));
     }
     pb.exportNames = exportNames;
     return pb;
   }
 }