dart2js: Use frequency of occurence to sort metadata indices.

pkg/compiler/lib/src/dump_info.dart

Index: pkg/compiler/lib/src/dump_info.dart
diff --git a/pkg/compiler/lib/src/dump_info.dart b/pkg/compiler/lib/src/dump_info.dart
index fb26f0c714ec0a7aa6993e90210f7de754ce5be8..d03880097b11799ec0af33e7187f1b2bd810e23a 100644
--- a/pkg/compiler/lib/src/dump_info.dart
+++ b/pkg/compiler/lib/src/dump_info.dart
@@ -494,19 +494,10 @@ class DumpInfoTask extends CompilerTask {
     }
   }
 
-  // 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)