dart2js: Use frequency of occurence to sort metadata indices.

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

 // Copyright (c) 2014, 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 dart2js.js_emitter.program_builder;
 
 import 'js_emitter.dart' show computeMixinClass;
 import 'model.dart';
 
 import '../common.dart';
@@ skipping 554 matching lines @@
         requiredParameterCount: requiredParameterCount,
         optionalParameterDefaultValues: optionalParameterDefaultValues,
         functionType: functionType);
   }
 
   js.Expression _generateFunctionType(DartType type, OutputUnit outputUnit) {
     if (type.containsTypeVariables) {
       js.Expression thisAccess = js.js(r'this.$receiver');
       return backend.rti.getSignatureEncoding(type, thisAccess);
     } else {
-      return js.number(backend.emitter.metadataCollector.
-          reifyTypeForOutputUnit(type, outputUnit));
+      return backend.emitter.metadataCollector
+          .reifyTypeForOutputUnit(type, outputUnit);
     }
   }
 
   List<ParameterStubMethod> _generateParameterStubs(MethodElement element,
                                                     bool canTearOff) {
 
     if (!_methodNeedsStubs(element)) return const <ParameterStubMethod>[];
 
     ParameterStubGenerator generator =
         new ParameterStubGenerator(_compiler, namer, backend);
@@ skipping 168 matching lines @@
       _registry.registerConstant(outputUnit, constantValue);
       assert(!_constants.containsKey(constantValue));
       String name = namer.constantName(constantValue);
       String constantObject = namer.globalObjectForConstant(constantValue);
       Holder holder = _registry.registerHolder(constantObject);
       Constant constant = new Constant(name, holder, constantValue);
       _constants[constantValue] = constant;
     }
   }
 }