Issue 28149. Don't include non-Dart file into FileState.

pkg/analyzer/test/src/dart/analysis/file_state_test.dart

 // Copyright (c) 2016, 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:convert';
 import 'dart:typed_data';
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/source/package_map_resolver.dart';
@@ skipping 306 matching lines @@
 
     expect(file.partedFiles, hasLength(1));
     expect(file.partedFiles[0].path, a4);
     expect(file.partedFiles[0].uri, FastUri.parse('package:aaa/a4.dart'));
 
     expect(file.directReferencedFiles, hasLength(5));
 
     expect(fileSystemState.getFilesForPath(a1), [file]);
   }
 
+  test_getFileForPath_onlyDartFiles() {
+    String a = _p('/test/lib/a.dart');
+    String b = _p('/test/lib/b.dart');
+    String c = _p('/test/lib/c.dart');
+    String d = _p('/test/lib/d.dart');
+    provider.newFile(
+        a,
+        r'''
+library lib;
+import 'dart:math';
+import 'b.dart';
+import 'not_dart.txt';
+export 'c.dart';
+export 'not_dart.txt';
+part 'd.dart';
+part 'not_dart.txt';
+''');
+    FileState file = fileSystemState.getFileForPath(a);
+    expect(file.importedFiles.map((f) => f.path), [b]);
+    expect(file.exportedFiles.map((f) => f.path), [c]);
+    expect(file.partedFiles.map((f) => f.path), [d]);
+    expect(fileSystemState.knownFilePaths, unorderedEquals([a, b, c, d]));
+  }
+
   test_getFileForPath_part() {
     String a1 = _p('/aaa/lib/a1.dart');
     String a2 = _p('/aaa/lib/a2.dart');
     provider.newFile(
         a1,
         r'''
 library a1;
 part 'a2.dart';
 ''');
     provider.newFile(
@@ skipping 316 matching lines @@
   void _assertTransitiveFiles(FileState file, List<FileState> expected) {
     expect(file.transitiveFiles, unorderedEquals(expected));
   }
 
   String _p(String path) => provider.convertPath(path);
 
   static String _md5(String content) {
     return hex.encode(md5.convert(UTF8.encode(content)).bytes);
   }
 }