Print the location of duplicated elements.

dart/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 510 matching lines @@
           compiler.withCurrentElement(element, () {
             compiler.reportError(new Identifier(element.position()),
             'duplicated import');
           });
         }
       });
     } else {
       importedLibrary.forEachExport((Element element) {
         compiler.withCurrentElement(element, () {
           if (combinatorFilter.exclude(element)) return;
-          importingLibrary.addImport(element, compiler);
+          importingLibrary.addImport(element, import, compiler);
         });
       });
     }
   }
 }
 
 /**
  * The combinator filter computed from an export tag and the library dependency
  * node for the library that declared the export tag. This represents an edge in
  * the library dependency graph.
@@ skipping 289 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();
   }
 }