Add @overrides to (a lot of) analyzer.

pkg/analyzer/example/parser_driver.dart

Index: pkg/analyzer/example/parser_driver.dart
diff --git a/pkg/analyzer/example/parser_driver.dart b/pkg/analyzer/example/parser_driver.dart
index c302e4140938b2a8e460d635879b7bc6ac981f6e..ccc5bb9d876efd63b3f1f09c934838a0b9592c9d 100644
--- a/pkg/analyzer/example/parser_driver.dart
+++ b/pkg/analyzer/example/parser_driver.dart
@@ -43,6 +43,7 @@ _parse(File file) {
 }
 
 class _ASTVisitor extends GeneralizingAstVisitor {
+  @override
   visitNode(AstNode node) {
     print('${node.runtimeType} : <"$node">');
     return super.visitNode(node);
@@ -52,5 +53,6 @@ class _ASTVisitor extends GeneralizingAstVisitor {
 class _ErrorCollector extends AnalysisErrorListener {
   List<AnalysisError> errors;
   _ErrorCollector() : errors = new List<AnalysisError>();
+  @override
   onError(error) => errors.add(error);
 }