Some preliminary support for quasi-generics

lib/runtime/dart/convert.js

 dart_library.library('dart/convert', null, /* Imports */[
   "dart_runtime/dart",
   'dart/core',
   'dart/async',
   'dart/typed_data',
   'dart/_internal',
   'dart/collection'
 ], /* Lazy imports */[
 ], function(exports, dart, core, async, typed_data, _internal, collection) {
   'use strict';
@@ skipping 27 matching lines @@
       })
     });
     return Codec;
   });
   let Codec = Codec$();
   class Encoding extends Codec$(core.String, core.List$(core.int)) {
     Encoding() {
       super.Codec();
     }
     decodeStream(byteStream) {
-      return dart.as(byteStream.transform(this.decoder).fold(new core.StringBuffer(), dart.fn((buffer, string) => ((() => {
+      return byteStream.transform(this.decoder).fold(new core.StringBuffer(), dart.fn((buffer, string) => ((() => {
         dart.dsend(buffer, 'write', string);
         return buffer;
-      })()))).then(dart.fn(buffer => dart.toString(buffer), core.String, [dart.dynamic])), async.Future$(core.String));
+      })()))).then(dart.fn(buffer => dart.toString(buffer), core.String, [dart.dynamic]));
     }
     static getByName(name) {
       if (name == null)
         return null;
       name = name[dartx.toLowerCase]();
       return Encoding._nameToEncoding.get(name);
     }
   }
   dart.setSignature(Encoding, {
     constructors: () => ({Encoding: [Encoding, []]}),
@@ skipping 2833 matching lines @@
   exports.LineSplitter = LineSplitter;
   exports.StringConversionSink = StringConversionSink;
   exports.ClosableStringSink = ClosableStringSink;
   exports.UNICODE_REPLACEMENT_CHARACTER_RUNE = UNICODE_REPLACEMENT_CHARACTER_RUNE;
   exports.UNICODE_BOM_CHARACTER_RUNE = UNICODE_BOM_CHARACTER_RUNE;
   exports.Utf8Codec = Utf8Codec;
   exports.UTF8 = UTF8;
   exports.Utf8Encoder = Utf8Encoder;
   exports.Utf8Decoder = Utf8Decoder;
 });