anchor.diff:  library ddc.src.dart_sdk;
   
   import 'dart:convert' as convert;
  -import 'dart:io' show File, Platform, Process;
  +import 'dart:io' show File, Link, Platform, Process;
   import 'package:path/path.dart' as path;
   import 'package:analyzer/src/generated/engine.dart';
   import 'package:analyzer/src/generated/sdk.dart';
  
positive.code: 
    return null;
  }
  
  /// Dart SDK which contains a mock implementation of the SDK libraries. May be
  /// used to speed up execution when most of the core libraries is not needed.
  
negative.code:       new File(path.join(dirname, 'lib', '_internal', 'libraries.dart'))
        .existsSync();
  
    String executable = Platform.executable;
    if (path.split(executable).length == 1) {
      // TODO(sigmund,blois): make this cross-platform.
      // HACK: A single part, hope it's on the path.
      executable = Process
          .runSync('which', ['dart'], stdoutEncoding: convert.UTF8).stdout.trim();
      // In case Dart is symlinked (e.g. homebrew on Mac) follow symbolic links.
      var link = new Link(executable);
      if (link.existsSync()) {
        executable = link.resolveSymbolicLinksSync();
      }
      var sdkDir = path.dirname(path.dirname(executable));
      if (isSdkDir(sdkDir)) return sdkDir;
    }
  
    var dartDir = path.dirname(path.absolute(executable));
    // If there's a sub-dir named dart-sdk then we're most likely executing from
    // a dart enlistment build directory.
    if (isSdkDir(path.join(dartDir, 'dart-sdk'))) {
  