dart2js: complain about missing part-of tags.

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 operator[](Node node);
   Selector getSelector(Send send);
   DartType getType(Node node);
@@ skipping 500 matching lines @@
 
     SourceString name =
       Elements.deconstructConstructorName(member.name, holder);
 
     // If the name could not be deconstructed, this is is from a
     // factory method from a deprecated interface implementation.
     if (name == null) return;
 
     Element otherMember = holder.lookupLocalMember(name);
     if (otherMember != null) {
-      compiler.onDeprecatedFeature(member, 'conflicting constructor');
-      compiler.reportMessage(
-          compiler.spanFromElement(otherMember),
-          MessageKind.GENERIC.error(['This member conflicts with a'
-                                     ' constructor.']),
-          Diagnostic.INFO);
+      if (compiler.onDeprecatedFeature(member, 'conflicting constructor')) {
+        compiler.reportMessage(
+            compiler.spanFromElement(otherMember),
+            MessageKind.GENERIC.error(['This member conflicts with a'
+                                       ' constructor.']),
+            Diagnostic.INFO);
+      }
     }
   }
 
   void checkAbstractField(Element member) {
     // Only check for getters. The test can only fail if there is both a setter
     // and a getter with the same name, and we only need to check each abstract
     // field once, so we just ignore setters.
     if (!member.isGetter()) return;
 
     // Find the associated abstract field.
@@ skipping 2724 matching lines @@
     return e;
   }
 
   /// Assumed to be called by [resolveRedirectingFactory].
   Element visitReturn(Return node) {
     Node expression = node.expression;
     return finishConstructorReference(visit(expression),
                                       expression, expression);
   }
 }