Print the location of duplicated elements.

dart/sdk/lib/_internal/compiler/implementation/resolution/members.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 resolution;
 
 abstract class TreeElements {
   Element get currentElement;
   Set<Node> get superUses;
 
@@ skipping 1467 matching lines @@
       return type;
     }
 
     if (element == null) {
       type = reportFailureAndCreateType(
           MessageKind.CANNOT_RESOLVE_TYPE, {'typeName': node.typeName});
     } else if (element.isAmbiguous()) {
       AmbiguousElement ambiguous = element;
       type = reportFailureAndCreateType(
           ambiguous.messageKind, ambiguous.messageArguments);
+      ambiguous.diagnose(visitor.mapping.currentElement, compiler);
     } else if (!element.impliesType()) {
       type = reportFailureAndCreateType(
           MessageKind.NOT_A_TYPE, {'node': node.typeName});
     } else {
       if (identical(element, compiler.types.voidType.element) ||
           identical(element, compiler.types.dynamicType.element)) {
         type = checkNoTypeArguments(element.computeType(compiler));
       } else if (element.isClass()) {
         ClassElement cls = element;
         compiler.resolver._ensureClassWillBeResolved(cls);
@@ skipping 216 matching lines @@
       if (!inInstanceContext && result.isInstanceMember()) {
         compiler.reportErrorCode(
             node, MessageKind.NO_INSTANCE_AVAILABLE, {'name': name});
         return new ErroneousElementX(MessageKind.NO_INSTANCE_AVAILABLE,
                                      {'name': name},
                                      name, enclosingElement);
       } else if (result.isAmbiguous()) {
         AmbiguousElement ambiguous = result;
         compiler.reportErrorCode(
             node, ambiguous.messageKind, ambiguous.messageArguments);
+        ambiguous.diagnose(enclosingElement, compiler);
         return new ErroneousElementX(ambiguous.messageKind,
                                      ambiguous.messageArguments,
                                      name, enclosingElement);
       }
     }
     return result;
   }
 
   // Create, or reuse an already created, statement element for a statement.
   TargetElement getOrCreateTargetElement(Node statement) {
@@ skipping 2286 matching lines @@
     return e;
   }
 
   /// Assumed to be called by [resolveRedirectingFactory].
   Element visitReturn(Return node) {
     Node expression = node.expression;
     return finishConstructorReference(visit(expression),
                                       expression, expression);
   }
 }