Add a static method decode to StringDecoder

tests/standalone/io/string_decoder_test.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.
 
 import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 
-void test() {
+void testTransform() {
   // Code point U+10FFFF is the largest code point supported by Dart.
   var controller = new StreamController(sync: true);
   controller.add([0xf0, 0x90, 0x80, 0x80]);  // U+10000
   controller.add([0xf4, 0x8f, 0xbf, 0xbf]);  // U+10FFFF
   controller.add([0xf4, 0x90, 0x80, 0x80]);  // U+110000
   controller.add([0xfa, 0x80, 0x80, 0x80, 0x80]);  //  U+2000000
   controller.add([0xfd, 0x80, 0x80, 0x80, 0x80, 0x80]);  // U+40000000
   controller.close();
 
   var decoder = new StringDecoder(Encoding.UTF_8, '?'.codeUnitAt(0));
@@ skipping 13 matching lines @@
         Expect.equals(0xdc00, decoded.codeUnitAt(1));
         Expect.equals(0xdbff, decoded.codeUnitAt(2));
         Expect.equals(0xdfff, decoded.codeUnitAt(3));
         Expect.equals(replacementChar, decoded.codeUnitAt(4));
         Expect.equals(replacementChar, decoded.codeUnitAt(5));
         Expect.equals(replacementChar, decoded.codeUnitAt(6));
         Expect.equals(replacementChar, decoded.codeUnitAt(7));
       });
 }
 
+void testDecode() {
+  // Code point U+10FFFF is the largest code point supported by Dart.
+  var controller = new StreamController(sync: true);
+  controller.add([0xf0, 0x90, 0x80, 0x80]);  // U+10000
+  controller.add([0xf4, 0x8f, 0xbf, 0xbf]);  // U+10FFFF
+  controller.add([0xf4, 0x90, 0x80, 0x80]);  // U+110000
+  controller.add([0xfa, 0x80, 0x80, 0x80, 0x80]);  //  U+2000000
+  controller.add([0xfd, 0x80, 0x80, 0x80, 0x80, 0x80]);  // U+40000000
+  controller.close();
+
+  StringDecoder.decode(controller.stream,
+                       Encoding.UTF_8,
+                       '?'.codeUnitAt(0)).then((decoded) {
+    Expect.equals(8, decoded.length);
+
+    var replacementChar = '?'.codeUnitAt(0);
+    Expect.equals(0xd800, decoded.codeUnitAt(0));
+    Expect.equals(0xdc00, decoded.codeUnitAt(1));
+    Expect.equals(0xdbff, decoded.codeUnitAt(2));
+    Expect.equals(0xdfff, decoded.codeUnitAt(3));
+    Expect.equals(replacementChar, decoded.codeUnitAt(4));
+    Expect.equals(replacementChar, decoded.codeUnitAt(5));
+    Expect.equals(replacementChar, decoded.codeUnitAt(6));
+    Expect.equals(replacementChar, decoded.codeUnitAt(7));
+  });
+}
+
 void testInvalid() {
   void invalid(var bytes, var outputLength) {
     var controller = new StreamController(sync: true);
     controller.add(bytes);
     controller.close();
     controller.stream.transform(new StringDecoder()).listen((string) {
       Expect.equals(outputLength, string.length);
       for (var i = 0; i < outputLength; i++) {
         Expect.equals(0xFFFD, string.codeUnitAt(i));
       }
     });
   }
 
   invalid([0x80], 1);
   invalid([0xff], 1);
   invalid([0xf0, 0xc0], 1);
   invalid([0xc0, 0x80], 1);
   invalid([0xfd, 0x80, 0x80], 3); // Unfinished encoding.
 }
 
 void main() {
-  test();
+  testTransform();
+  testDecode();
   testInvalid();
 }