Create a wrapper class to handle CompilerOptions in a uniform way.

pkg/front_end/lib/dependency_grapher.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.
 
 import 'dart:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/dart/scanner/reader.dart';
 import 'package:analyzer/src/generated/parser.dart';
 import 'package:front_end/file_system.dart';
 import 'package:front_end/src/async_dependency_walker.dart';
+import 'package:front_end/src/base/processed_options.dart';
 import 'package:front_end/src/base/uri_resolver.dart';
 import 'package:front_end/src/scanner/scanner.dart';
-import 'package:package_config/packages_file.dart' as package_config;
 
 import 'compiler_options.dart';
 
 /// Generates a representation of the dependency graph of a program.
 ///
 /// Given the Uri of one or more files, this function follows `import`,
 /// `export`, and `part` declarations to discover a graph of all files involved
 /// in the program.
 Future<Graph> graphForProgram(
     List<Uri> sources, CompilerOptions options) async {
-  Map<String, Uri> packages;
-  if (options.packagesFilePath == null) {
-    throw new UnimplementedError(); // TODO(paulberry): search for .packages
-  } else if (options.packagesFilePath.isEmpty) {
-    packages = {};
-  } else {
-    var contents = await options.fileSystem
-        .entityForPath(options.packagesFilePath)
-        .readAsBytes();
-    var baseLocation =
-        options.fileSystem.context.toUri(options.packagesFilePath);
-    packages = package_config.parse(contents, baseLocation);
-  }
-  var sdkLibraries = <String, Uri>{}; // TODO(paulberry): support SDK libraries
-  var uriResolver =
-      new UriResolver(packages, sdkLibraries, options.fileSystem.context);
-  var walker = new _Walker(options.fileSystem, uriResolver, options.compileSdk);
+  var processedOptions = new ProcessedOptions(options);
+  var uriResolver = await processedOptions.getUriResolver();
+  var walker = new _Walker(processedOptions.fileSystem, uriResolver, processedOptions.compileSdk);
   var startingPoint = new _StartingPoint(walker, sources);
   await walker.walk(startingPoint);
   return walker.graph;
 }
 
 /// A representation of the dependency graph of a program.
 ///
 /// Not intended to be extended, implemented, or mixed in by clients.
 class Graph {
   /// A list of all library cycles in the program, in topologically sorted order
@@ skipping 133 matching lines @@
           handleDependency(referencedUri);
         }
       }
     }
     if (!coreUriFound) {
       handleDependency(dartCoreUri);
     }
     return dependencies;
   }
 }