Make Analyzer, VM and dart2js accept URI strings as part-of library identifier.

pkg/analyzer/lib/src/task/dart.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 analyzer.src.task.dart;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_resolution_map.dart';
@@ skipping 1608 matching lines @@
             }
           }
           if (entryPoint == null) {
             entryPoint = _findEntryPoint(partElement);
           }
           directive.element = partElement;
           sourcedCompilationUnits.add(partElement);
         }
       }
     }
-    if (hasPartDirective && libraryNameNode == null) {
+    if (hasPartDirective && libraryNameNode == null &&
+        !context.analysisOptions.enableUriInPartOf) {
       errors.add(new AnalysisError(librarySource, 0, 0,
           ResolverErrorCode.MISSING_LIBRARY_DIRECTIVE_WITH_PART));
     }
     //
     // Create and populate the library element.
     //
     AnalysisContext owningContext = context;
     if (context is InternalAnalysisContext) {
       InternalAnalysisContext internalContext = context;
       owningContext = internalContext.getContextFor(librarySource);
@@ skipping 4914 matching lines @@
 
   @override
   bool moveNext() {
     if (_newSources.isEmpty) {
       return false;
     }
     currentTarget = _newSources.removeLast();
     return true;
   }
 }