Move PackageMapUriResolver into analyzer.

pkg/analyzer/lib/source/package_map_resolver.dart

 // Copyright (c) 2014, 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 resolver.package;
+library source.package_map_resolver;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/generated/source.dart';
 
 
 /**
  * A [UriResolver] implementation for the `package:` scheme that uses a map of
  * package names to their directories.
  */
 class PackageMapUriResolver extends UriResolver {
@@ skipping 58 matching lines @@
           Resource result = packageDir.getChild(relPath);
           if (result is File && result.exists) {
             return result.createSource(UriKind.PACKAGE_URI);
           }
         }
       }
     }
     // Return a NonExistingSource instance.
     // This helps provide more meaningful error messages to users
     // (a missing file error, as opposed to an invalid URI error).
-    // TODO(scheglov) move NonExistingSource to "source.dart"
     return new NonExistingSource(uri.toString(), UriKind.PACKAGE_URI);
   }
 
   /**
    * Returns `true` if [uri] is a `package` URI.
    */
   static bool isPackageUri(Uri uri) {
     return uri.scheme == PACKAGE_SCHEME;
   }
 }