Fix handling of empty .analysis_options files and test this case

pkg/analyzer/test/source/analysis_options_provider_test.dart

Index: pkg/analyzer/test/source/analysis_options_provider_test.dart
diff --git a/pkg/analyzer/test/source/analysis_options_provider_test.dart b/pkg/analyzer/test/source/analysis_options_provider_test.dart
index b20027846e6638a54917d1744cadd142b6711319..35bbd85bbd54d264916399e85aadcf0f644d5eb9 100644
--- a/pkg/analyzer/test/source/analysis_options_provider_test.dart
+++ b/pkg/analyzer/test/source/analysis_options_provider_test.dart
@@ -41,15 +41,31 @@ main() {
       expect(options.length, equals(0));
     });
   });
+  group('AnalysisOptionsProviderEmpty', () {
+    setUp(() {
+      buildResourceProvider(true);
+    });
+    tearDown(() {
+      clearResourceProvider();
+    });
+    test('test_simple', () {
+      var optionsProvider = new AnalysisOptionsProvider();
+      Map<String, YamlNode> options =
+          optionsProvider.getOptions(resourceProvider.getFolder('/'));
+    });
+  });
 }
 
 MemoryResourceProvider resourceProvider;
 
-buildResourceProvider() {
+buildResourceProvider([bool emptyAnalysisOptions = false]) {
   resourceProvider = new MemoryResourceProvider();
   resourceProvider.newFolder('/empty');
   resourceProvider.newFolder('/tmp');
-  resourceProvider.newFile(
+  if (emptyAnalysisOptions) {
+    resourceProvider.newFile('/.analysis_options', r'''''');
+  } else {
+    resourceProvider.newFile(
       '/.analysis_options',
       r'''
 analyzer:
@@ -57,6 +73,8 @@ analyzer:
     - ignoreme.dart
     - 'sdk_ext/**'
 ''');
+  }
+
 }
 
 clearResourceProvider() {