dart2js: build metadata-types lazily in the new emitter.

pkg/compiler/lib/src/js_emitter/metadata_collector.dart

 // Copyright (c) 2013, 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.js_emitter;
 
 class MetadataCollector {
   final Compiler _compiler;
   final Emitter _emitter;
 
@@ skipping 94 matching lines @@
             (variable) {
               if (ignoreTypeVariables) return new jsAst.LiteralNull();
               return js.number(
                   _typeVariableHandler.reifyTypeVariable(
                       variable.element));
             },
             (TypedefType typedef) {
               return _backend.isAccessibleByReflection(typedef.element);
             });
 
+    if (representation is jsAst.LiteralString) {
+      // We don't want the representation to be a string, since we use
+      // strings as indicator for non-initialized types in the lazy emitter.
+      _compiler.internalError(
+          NO_LOCATION_SPANNABLE, 'reified types should not be strings.');
+    }
     return addTypeInOutputUnit(
         jsAst.prettyPrint(representation, _compiler).getText(), outputUnit);
   }
 
   int reifyName(String name) {
     return addGlobalMetadata('"$name"');
   }
 
   int addGlobalMetadata(String string) {
     return _globalMetadataMap.putIfAbsent(string, () {
       globalMetadata.add(string);
       return globalMetadata.length - 1;
     });
   }
 
   int addTypeInOutputUnit(String compiledType, OutputUnit outputUnit) {
     if (_typesMap[outputUnit] == null) {
       _typesMap[outputUnit] = <String, int>{};
     }
     return _typesMap[outputUnit].putIfAbsent(compiledType, () {
 
-      if (types[outputUnit] == null)
+      if (types[outputUnit] == null) {
         types[outputUnit] = <String>[];
+      }
 
       types[outputUnit].add(compiledType);
       return types[outputUnit].length - 1;
     });
   }
 
   List<int> computeMetadata(FunctionElement element) {
     return _compiler.withCurrentElement(element, () {
       if (!_mustEmitMetadataFor(element)) return const <int>[];
       List<int> metadata = <int>[];
       Link link = element.metadata;
       // TODO(ahe): Why is metadata sometimes null?
       if (link != null) {
         for (; !link.isEmpty; link = link.tail) {
           metadata.add(reifyMetadata(link.head));
         }
       }
       return metadata;
     });
   }
 }