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

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

Index: pkg/analyzer/test/src/dart/analysis/driver_test.dart
diff --git a/pkg/analyzer/test/src/dart/analysis/driver_test.dart b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
index 24eb692f3212b72f14c55b5d2ef4fbcb9cd6a38d..05b7cb2600995a945fd3e55c80bbf3fe19d54ac0 100644
--- a/pkg/analyzer/test/src/dart/analysis/driver_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
@@ -1122,6 +1122,11 @@ main() {
         unorderedEquals(['foo', 'main']));
   }
 
+  test_getUnitElement_notDart() async {
+    CompilationUnitElement unit = await driver.getUnitElement('foo.txt');
+    expect(unit, isNull);
+  }
+
   test_hasFilesToAnalyze() async {
     // No files yet, nothing to analyze.
     expect(driver.hasFilesToAnalyze, isFalse);