anchor.diff:  import 'package:analyzer/src/generated/source.dart';
   import 'package:analyzer/src/summary/package_bundle_reader.dart';
   import 'package:analyzer/src/summary/pub_summary.dart';
  +import 'package:analyzer/src/summary/summary_sdk.dart';
   import 'package:analyzer/src/task/options.dart';
   import 'package:package_config/packages.dart';
   import 'package:package_config/packages_file.dart';
  
positive.code:    * or `null` if the normal lookup mechanism should be used.
     */
    String defaultPackagesDirectoryPath;
  
    /**
     * The file path of the analysis options file that should be used in place of
  
negative.code:    */
    DartSdk findSdk(
        Map<String, List<Folder>> packageMap, AnalysisOptions options) {
      if (dartSdkSummaryPath != null) {
        return new SummaryBasedDartSdk(dartSdkSummaryPath, options.strongMode);
      } else if (packageMap != null) {
        SdkExtensionFinder extFinder = new SdkExtensionFinder(packageMap);
        List<String> extFilePaths = extFinder.extensionFilePaths;
        EmbedderYamlLocator locator = new EmbedderYamlLocator(packageMap);
  