Require two type arguments for map literals (issue 4522).

lib/compiler/implementation/dart2js.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.
 
 #library('dart2js');
 
 #import('dart:io');
 #import('dart:uri');
 #import('dart:utf');
 
@@ skipping 133 matching lines @@
   if (wantHelp) helpAndExit(verbose);
 
   if (arguments.isEmpty()) {
     helpAndFail('Error: No Dart file specified.');
   }
   if (arguments.length > 1) {
     var extra = arguments.getRange(1, arguments.length - 1);
     helpAndFail('Error: Extra arguments: ${Strings.join(extra, " ")}');
   }
 
-  Map<String, SourceFile> sourceFiles = <SourceFile>{};
+  Map<String, SourceFile> sourceFiles = <String, SourceFile>{};
   int dartBytesRead = 0;
 
   Future<String> provider(Uri uri) {
     if (uri.scheme != 'file') {
       throw new IllegalArgumentException(uri);
     }
     String source;
     try {
       source = readAll(uriPathToNative(uri.path));
     } catch (FileIOException ex) {
@@ skipping 209 matching lines @@
     } catch (var ignored) {
       print('Internal error: error while printing exception');
     }
     try {
       print(trace);
     } finally {
       exit(253); // 253 is recognized as a crash by our test scripts.
     }
   }
 }