Make IOSink implement StringSink

sdk/lib/io/http_headers.dart

Index: sdk/lib/io/http_headers.dart
diff --git a/sdk/lib/io/http_headers.dart b/sdk/lib/io/http_headers.dart
index b2b522b3b3e900f84131bb909c9efb8d2feb9c02..272eada9f23ab359d949f4cf6fcc479acf447ece 100644
--- a/sdk/lib/io/http_headers.dart
+++ b/sdk/lib/io/http_headers.dart
@@ -350,7 +350,7 @@ class _HttpHeaders implements HttpHeaders {
     var bufferPos = 0;
 
     void writeBuffer() {
-      sink.add(buffer.getRange(0, bufferPos));
+      sink.writeBytes(buffer.getRange(0, bufferPos));
       bufferPos = 0;
     }
 
@@ -621,6 +621,9 @@ class _HeaderValue implements HeaderValue {
 
 
 class _ContentType extends _HeaderValue implements ContentType {
+  String _primaryType = "";
+  String _subType = "";
+
   _ContentType(String primaryType,
                String subType,
                String charset,
@@ -639,7 +642,7 @@ class _ContentType extends _HeaderValue implements ContentType {
     }
   }
 
-    _ContentType.fromString(String value) : super.fromString(value) {
+  _ContentType.fromString(String value) : super.fromString(value) {
     int index = _value.indexOf("/");
     if (index == -1 || index == (_value.length - 1)) {
       _primaryType = _value.trim().toLowerCase();
@@ -656,8 +659,20 @@ class _ContentType extends _HeaderValue implements ContentType {
 
   String get charset => parameters["charset"];
 
-  String _primaryType = "";
-  String _subType = "";
+  Encoding get encoding {
+    if (charset == null ||
+        charset == "iso-8859-1" ||
+        charset == "iso_8859-1" ||
+        charset == "latin1") {
+      return Encoding.ISO_8859_1;
+    } else if (charset == "utf-8") {
+      return Encoding.UTF_8;
+    } else if (charset == "us-ascii") {
+      return Encoding.ASCII;
+    } else {
+      return null;
+    }
+  }
 }