Implement also 'execution.mapUri' for file to URI.

pkg/analysis_server/test/integration/execution/map_uri_test.dart

 // Copyright (c) 2017, 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 'dart:async';
-
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../integration_tests.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(MapUriTest);
     defineReflectiveTests(MapUriTest_Driver);
   });
 }
 
 class AbstractMapUriTest extends AbstractAnalysisServerIntegrationTest {
-  Future test_mapUri() async {
+  test_mapUri() async {
     String pathname = sourcePath('lib/main.dart');
     writeFile(pathname, '// dummy');
     writeFile(sourcePath('.packages'), 'foo:lib/');
     standardAnalysisSetup();
 
     String contextId =
         (await sendExecutionCreateContext(sourceDirectory.path))?.id;
-    ExecutionMapUriResult result =
-        await sendExecutionMapUri(contextId, uri: 'package:foo/main.dart');
-    expect(result.file, pathname);
+
+    {
+      ExecutionMapUriResult result =
+          await sendExecutionMapUri(contextId, uri: 'package:foo/main.dart');
+      expect(result.file, pathname);
+    }
+
+    {
+      ExecutionMapUriResult result =
+          await sendExecutionMapUri(contextId, file: pathname);
+      expect(result.uri, 'package:foo/main.dart');
+    }
   }
 }
 
 @reflectiveTest
 class MapUriTest extends AbstractMapUriTest {}
 
 @reflectiveTest
 class MapUriTest_Driver extends AbstractMapUriTest {
   @override
   bool get enableNewAnalysisDriver => true;
 }