Avoid reparsing metadata expressions

pkg/compiler/lib/src/js_backend/type_variable_handler.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 js_backend;
 
 /**
  * Handles construction of TypeVariable constants needed at runtime.
  */
 class TypeVariableHandler {
@@ skipping 106 matching lines @@
 
   /**
    * Adds [c] to [emitter.metadataCollector] and returns the index pointing to
    * the entry.
    *
    * If the corresponding type variable has already been encountered an
    * entry in the list has already been reserved and the constant is added
    * there, otherwise a new entry for [c] is created.
    */
   int _reifyTypeVariableConstant(ConstantValue c, TypeVariableElement variable) {
-    String name = jsAst.prettyPrint(_task.constantReference(c),
-                                    _compiler).getText();
+    jsAst.Expression name = _task.constantReference(c);
     int index;
     if (_typeVariableConstants.containsKey(variable)) {
       index = _typeVariableConstants[variable];
       _metadataCollector.globalMetadata[index] = name;
     } else {
       index = _metadataCollector.addGlobalMetadata(name);
       _typeVariableConstants[variable] = index;
     }
     return index;
   }
 
   /**
    * Returns the index pointing to the constant in [emitter.metadataCollector]
    * representing this type variable.
    *
    * If the constant has not yet been constructed, an entry is  allocated in
    * the global metadata list and the index pointing to this entry is returned.
    * When the corresponding constant is constructed later,
    * [reifyTypeVariableConstant] will be called and the constant will be added
    * on the allocated entry.
    */
   int reifyTypeVariable(TypeVariableElement variable) {
     if (_typeVariableConstants.containsKey(variable)) {
       return _typeVariableConstants[variable];
     }
 
     // TODO(15613): Remove quotes.
-    _metadataCollector.globalMetadata.add('"Placeholder for ${variable}"');
+    _metadataCollector.globalMetadata.add(js('"Placeholder for ${variable}"'));
     return _typeVariableConstants[variable] =
         _metadataCollector.globalMetadata.length - 1;
   }
 
   List<int> typeVariablesOf(ClassElement classElement) {
     List<int> result = _typeVariables[classElement];
     if (result == null) {
       result = const <int>[];
     }
     return result;
   }
 }