dart2js: Use frequency of occurence to sort metadata indices.

pkg/compiler/lib/src/js_emitter/old_emitter/class_builder.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;
 
 /**
  * A data structure for collecting fragments of a class definition.
  */
 class ClassBuilder {
   final List<jsAst.Property> properties = <jsAst.Property>[];
-  final List<String> fields = <String>[];
+  final List<jsAst.Literal> fields = <jsAst.Literal>[];
 
   String superName;
-  String functionType;
+  jsAst.Node functionType;
   List<jsAst.Node> fieldMetadata;
 
   final Element element;
   final Namer namer;
 
   ClassBuilder(this.element, this.namer);
 
   jsAst.Property addProperty(String name, jsAst.Expression value) {
     jsAst.Property property = new jsAst.Property(js.string(name), value);
     properties.add(property);
     return property;
   }
 
-  void addField(String field) {
+  void addField(jsAst.Literal field) {
     fields.add(field);
   }
 
   static String functionTypeEncodingDescription =
       'For simple function types the function type is stored in the metadata '
       'and the index is encoded into the superclass field.';
 
   static String fieldEncodingDescription =
       'Fields are encoded as a comma separated list. If there is a superclass '
       '(and possibly a function type encoding) the fields are separated from '
       'the superclass by a semicolon.';
 
-  jsAst.ObjectInitializer toObjectInitializer(
+  jsAst.ObjectInitializer toObjectInitializer(Compiler compiler,

[karlklose, 2015/05/28 09:39:53]

The parameter 'compiler' seems to be unsued.

[herhut, 2015/06/01 12:09:42]

True. Removed.

       {bool emitClassDescriptor: true}) {
-    StringBuffer buffer = new StringBuffer();
+    List<jsAst.Literal> parts = <jsAst.Literal>[];
     if (superName != null) {
-      buffer.write(superName);
+      parts.add(js.stringPart(superName));
       if (functionType != null) {
         // See [functionTypeEncodingDescription] above.
-        buffer.write(':$functionType');
+        parts.add(js.stringPart(':'));
+        parts.add(functionType);
       }
-      buffer.write(';');
+      parts.add(js.stringPart(';'));
     }
     // See [fieldEncodingDescription] above.
-    buffer.writeAll(fields, ',');
-    var classData = js.string('$buffer');
+    parts.addAll(js.joinLiterals(fields, js.stringPart(',')));
+    var classData = js.concatenateStrings(parts, addQuotes: true);
     if (fieldMetadata != null) {
       // If we need to store fieldMetadata, classData is turned into an array,
       // and the field metadata is appended. So if classData is just a string,
       // there is no field metadata.
       classData =
           new jsAst.ArrayInitializer([classData]..addAll(fieldMetadata));
     }
     List<jsAst.Property> fieldsAndProperties;
     if (emitClassDescriptor) {
       fieldsAndProperties = <jsAst.Property>[];
       fieldsAndProperties.add(
           new jsAst.Property(
               js.string(namer.classDescriptorProperty), classData));
       fieldsAndProperties.addAll(properties);
     } else {
       fieldsAndProperties = properties;
     }
     return new jsAst.ObjectInitializer(fieldsAndProperties, isOneLiner: false);
   }
 }