a few small refactorings to closure workarounds

lib/runtime/dart/convert.js

Index: lib/runtime/dart/convert.js
diff --git a/lib/runtime/dart/convert.js b/lib/runtime/dart/convert.js
index baa6afa28f84fe08a2ab886fc27460ad04db0c07..d5bcdfeb792859dbfd03f197fd565579b2a52682 100644
--- a/lib/runtime/dart/convert.js
+++ b/lib/runtime/dart/convert.js
@@ -9,6 +9,7 @@ dart_library.library('dart/convert', null, /* Imports */[
 ], function(exports, dart, core, async, typed_data, _internal, collection) {
   'use strict';
   let dartx = dart.dartx;
+  const _allowInvalid = Symbol('_allowInvalid');
   const Codec$ = dart.generic(function(S, T) {
     class Codec extends core.Object {
       Codec() {
@@ -68,7 +69,6 @@ dart_library.library('dart/convert', null, /* Imports */[
     },
     set _nameToEncoding(_) {}
   });
-  const _allowInvalid = Symbol('_allowInvalid');
   class AsciiCodec extends Encoding {
     AsciiCodec(opts) {
       let allowInvalid = opts && 'allowInvalid' in opts ? opts.allowInvalid : false;
@@ -100,6 +100,7 @@ dart_library.library('dart/convert', null, /* Imports */[
   });
   const ASCII = dart.const(new AsciiCodec());
   const _ASCII_MASK = 127;
+  const _subsetMask = Symbol('_subsetMask');
   const Converter$ = dart.generic(function(S, T) {
     class Converter extends core.Object {
       Converter() {
@@ -129,7 +130,6 @@ dart_library.library('dart/convert', null, /* Imports */[
     return Converter;
   });
   let Converter = Converter$();
-  const _subsetMask = Symbol('_subsetMask');
   class _UnicodeSubsetEncoder extends Converter$(core.String, core.List$(core.int)) {
     _UnicodeSubsetEncoder(subsetMask) {
       this[_subsetMask] = subsetMask;
@@ -178,6 +178,7 @@ dart_library.library('dart/convert', null, /* Imports */[
   dart.setSignature(AsciiEncoder, {
     constructors: () => ({AsciiEncoder: [AsciiEncoder, []]})
   });
+  const _sink = Symbol('_sink');
   class StringConversionSinkMixin extends core.Object {
     add(str) {
       return this.addSlice(str, 0, str[dartx.length], false);
@@ -198,7 +199,6 @@ dart_library.library('dart/convert', null, /* Imports */[
     })
   });
   class StringConversionSinkBase extends StringConversionSinkMixin {}
-  const _sink = Symbol('_sink');
   class _UnicodeSubsetEncoderSink extends StringConversionSinkBase {
     _UnicodeSubsetEncoderSink(subsetMask, sink) {
       this[_subsetMask] = subsetMask;
@@ -297,6 +297,7 @@ dart_library.library('dart/convert', null, /* Imports */[
     constructors: () => ({AsciiDecoder: [AsciiDecoder, [], {allowInvalid: core.bool}]}),
     methods: () => ({startChunkedConversion: [ByteConversionSink, [core.Sink$(core.String)]]})
   });
+  const _utf8Sink = Symbol('_utf8Sink');
   const ChunkedConversionSink$ = dart.generic(function(T) {
     class ChunkedConversionSink extends core.Object {
       ChunkedConversionSink() {
@@ -345,7 +346,6 @@ dart_library.library('dart/convert', null, /* Imports */[
   dart.setSignature(ByteConversionSinkBase, {
     methods: () => ({addSlice: [dart.void, [core.List$(core.int), core.int, core.int, core.bool]]})
   });
-  const _utf8Sink = Symbol('_utf8Sink');
   class _ErrorHandlingAsciiDecoderSink extends ByteConversionSinkBase {
     _ErrorHandlingAsciiDecoderSink(utf8Sink) {
       this[_utf8Sink] = utf8Sink;