Handle exception from scanning.

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 263 matching lines @@
       }
       return TagState.NEXT[value];
     }
 
     bool importsDartCore = false;
     var libraryDependencies = new LinkBuilder<LibraryDependency>();
     Uri base = library.entryCompilationUnit.script.uri;
 
     // TODO(rnystrom): Remove .toList() here if #11523 is fixed.
     return Future.forEach(library.tags.reverse().toList(), (LibraryTag tag) {
-      compiler.withCurrentElement(library, () {
+      return compiler.withCurrentElement(library, () {
         if (tag.isImport) {
           Import import = tag;
           tagState = checkTag(TagState.IMPORT_OR_EXPORT, import);
           if (import.uri.dartString.slowToString() == 'dart:core') {
             importsDartCore = true;
           }
           libraryDependencies.addLast(import);
         } else if (tag.isExport) {
           tagState = checkTag(TagState.IMPORT_OR_EXPORT, tag);
           libraryDependencies.addLast(tag);
@@ skipping 575 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();
   }
 }