Handle clash of prefix/non-prefix imports.

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

 // Copyright (c) 2011, 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;
 
 const DONT_KNOW_HOW_TO_FIX = "";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 236 matching lines @@
 'future.dart':
 """
 library future;
 
 class Future {}""",
 
 'export.dart':
 """
 library export;
 
-export 'future.dart';"""}]);
+export 'future.dart';"""},
+
+         const {
+'main.dart':
+"""
+import 'future.dart' as prefix;
+import 'dart:async' as prefix; // This imports a class Future.
+
+void main() => new prefix.Future();""",
+
+'future.dart':
+"""
+library future;
+
+class Future {}"""}]);
 
 
   static const MessageKind HIDDEN_IMPLICIT_IMPORT = const MessageKind(
       "Warning: '#{name}' from library '#{hiddenUri}' is hidden by '#{name}' "
       "from library '#{hidingUri}'.",
       howToFix: "Try adding an explicit "
                 "'import \"#{hiddenUri}\" hide #{name}'.",
       examples: const [
           const {
 'main.dart':
@@ skipping 1136 matching lines @@
 
 class CompileTimeConstantError extends Diagnostic {
   CompileTimeConstantError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }
 
 class CompilationError extends Diagnostic {
   CompilationError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }