dart2js: Use frequency of occurence to sort metadata indices.

pkg/compiler/lib/src/dump_info.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.
 
 library dump_info;
 
 import 'dart:convert' show
     HtmlEscape,
     JsonEncoder,
     StringConversionSink,
@@ skipping 476 matching lines @@
 
   // Records the size of a dart AST node after it has been
   // pretty-printed into the output buffer.
   void recordAstSize(jsAst.Node node, int size) {
     if (isTracking(node)) {
       //TODO: should I be incrementing here instead?
       _nodeToSize[node] = size;
     }
   }
 
-  // Field names are treated differently by the dart compiler
-  // so they must be recorded seperately.
-  void recordFieldNameSize(Element element, int size) {
-    _fieldNameToSize[element] = size;
-  }
-
   // Returns the size of the source code that
   // was generated for an element.  If no source
   // code was produced, return 0.
   int sizeOf(Element element) {
-    if (_fieldNameToSize.containsKey(element)) {
-      return _fieldNameToSize[element];
-    }
     if (_elementToNodes.containsKey(element)) {
       return _elementToNodes[element]
         .map(sizeOfNode)
         .fold(0, (a, b) => a + b);
     } else {
       return 0;
     }
   }
 
   int sizeOfNode(jsAst.Node node) {
@@ skipping 122 matching lines @@
     ChunkedConversionSink<Object> sink =
       encoder.startChunkedConversion(
           new StringConversionSink.fromStringSink(buffer));
     sink.add(outJson);
     compiler.reportInfo(NO_LOCATION_SPANNABLE,
         const MessageKind(
             "View the dumped .info.json file at "
             "https://dart-lang.github.io/dump-info-visualizer"));
   }
 }