Revert "Allow import/export of libraries with no name."

sdk/lib/_internal/compiler/implementation/library_loader.dart

 // Copyright (c) 2012, 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.
 
 part of dart2js;
 
 /**
  * [CompilerTask] for loading libraries and setting up the import/export scopes.
  *
  * The library loader uses four different kinds of URIs in different parts of
@@ skipping 403 matching lines @@
   Future registerLibraryFromTag(LibraryDependencyHandler handler,
                                 LibraryElement library,
                                 LibraryDependency tag) {
     Uri base = library.entryCompilationUnit.script.uri;
     Uri resolvedUri = base.resolve(tag.uri.dartString.slowToString());
     return createLibrary(handler, library, resolvedUri, tag.uri, resolvedUri)
         .then((LibraryElement loadedLibrary) {
           if (loadedLibrary == null) return;
           compiler.withCurrentElement(library, () {
             handler.registerDependency(library, tag, loadedLibrary);
+
+            if (!loadedLibrary.hasLibraryName()) {
+              compiler.reportFatalError(
+                  tag == null ? null : tag.uri,
+                  MessageKind.GENERIC,
+                  {'text':
+                   'Error: No library name found in '
+                      '${loadedLibrary.canonicalUri}.'});
+            }
           });
         });
   }
 
   /**
    * Create (or reuse) a library element for the library specified by the
    * [resolvedUri].
    *
    * If a new library is created, the [handler] is notified.
    */
@@ skipping 425 matching lines @@
   }
 
   /**
    * Registers all top-level entities of [library] as starting point for the
    * fixed-point computation of the import/export scopes.
    */
   void registerLibraryExports(LibraryElement library) {
     nodeMap[library].registerInitialExports();
   }
 }