Implement support for application/x-www-form-urlencoded' form data in HttpBodyHandler.

sdk/lib/io/http_multipart_form_data_impl.dart

Index: sdk/lib/io/http_multipart_form_data_impl.dart
diff --git a/sdk/lib/io/http_multipart_form_data_impl.dart b/sdk/lib/io/http_multipart_form_data_impl.dart
index 4407bb527c2966e878ba7f70a9f6c9c40e3f6f51..b2279541cc428a274aae780bac501a5354967c1a 100644
--- a/sdk/lib/io/http_multipart_form_data_impl.dart
+++ b/sdk/lib/io/http_multipart_form_data_impl.dart
@@ -41,7 +41,7 @@ class _HttpMultipartFormData extends Stream implements HttpMultipartFormData {
           .transform(new StringDecoder(encoding))
           .expand((data) {
             buffer.write(data);
-            var out = _HttpUtils.parseHttpEntityString(buffer.toString());
+            var out = _HttpUtils.decodeHttpEntityString(buffer.toString());
             if (out != null) {
               buffer = new StringBuffer();
               return [out];