Validate that int values that we write to summaries are >= 0.

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 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/type.dart';
@@ skipping 488 matching lines @@
     return b;
   }
 
   /**
    * Serialize the given [importElement] yielding an [UnlinkedImportBuilder].
    * Also, add linked information about it to the [linkedImports] list.
    */
   UnlinkedImportBuilder serializeImport(ImportElement importElement) {
     UnlinkedImportBuilder b = new UnlinkedImportBuilder();
     b.isDeferred = importElement.isDeferred;
-    b.offset = importElement.nameOffset;
     b.combinators = importElement.combinators.map(serializeCombinator).toList();
     if (importElement.prefix != null) {
       b.prefixReference = serializePrefix(importElement.prefix);
       b.prefixOffset = importElement.prefix.nameOffset;
     }
     if (importElement.isSynthetic) {
       b.isImplicit = true;
     } else {
+      b.offset = importElement.nameOffset;
       b.uri = importElement.uri;
       b.uriOffset = importElement.uriOffset;
       b.uriEnd = importElement.uriEnd;
     }
     return b;
   }
 
   /**
    * Serialize the given [parameter] into an [UnlinkedParam].
    */
@@ skipping 452 matching lines @@
       exportNames.add(new LinkedExportNameBuilder(
           name: name,
           dependency: serializeDependency(dependentLibrary),
           unit: unit,
           kind: kind));
     }
     pb.exportNames = exportNames;
     return pb;
   }
 }