Change MultipartFile.fromFile to MultipartFile.fromPath in pkg/http.

pkg/http/test/multipart_test.dart

Index: pkg/http/test/multipart_test.dart
diff --git a/pkg/http/test/multipart_test.dart b/pkg/http/test/multipart_test.dart
index 9c83ce1d43d13c0a75e576afc539a183b086fb9a..9ebcb834bce2927da70ee56f1f471cdd37a0984b 100644
--- a/pkg/http/test/multipart_test.dart
+++ b/pkg/http/test/multipart_test.dart
@@ -8,6 +8,7 @@ import 'dart:async';
 import 'dart:io';
 import 'dart:utf';
 
+import 'package:pathos/path.dart' as path;
 import 'package:unittest/unittest.dart';
 import 'package:http/http.dart' as http;
 import 'package:http/src/utils.dart';
@@ -202,4 +203,26 @@ void main() {
         --{{boundary}}--
         '''));
   });
+
+  test('with a file from disk', () {
+    var tempDir = new Directory('').createTempSync();
+
+    expect(new Future.of(() {
+      var filePath = path.join(tempDir.path, 'test-file');
+      new File(filePath).writeAsStringSync('hello');
+      return http.MultipartFile.fromPath('file', filePath);
+    }).then((file) {
+      var request = new http.MultipartRequest('POST', dummyUrl);
+      request.files.add(file);
+
+      expect(request, bodyMatches('''
+        --{{boundary}}
+        content-type: application/octet-stream
+        content-disposition: form-data; name="file"; filename="test-file"
+
+        hello
+        --{{boundary}}--
+        '''));
+    }).whenComplete(() => tempDir.delete(recursive: true)), completes);
+  });
 }