Improve type information and minor clean up

pkg/analyzer/lib/src/services/lint.dart

 // Copyright (c) 2015, 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.
 
 library analyzer.src.services.lint;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/task/model.dart';
 import 'package:analyzer/task/model.dart';
 
 const List<Linter> _noLints = const <Linter>[];
 
 /// The descriptor used to associate lints with analysis contexts in
 /// configuration data.
 final ResultDescriptor<List<Linter>> CONFIGURED_LINTS_KEY =
     new ResultDescriptorImpl('configured.lints', _noLints);
 
 /// Shared lint registry.
 LintRegistry lintRegistry = new LintRegistry();
 
 /// Return lints associated with this [context], or an empty list if there are
 /// none.
 List<Linter> getLints(AnalysisContext context) =>
-    context.getConfigurationData(CONFIGURED_LINTS_KEY) as List<Linter> ??
-    _noLints;
+    context.getConfigurationData(CONFIGURED_LINTS_KEY) ?? _noLints;
 
 /// Associate these [lints] with the given [context].
 void setLints(AnalysisContext context, List<Linter> lints) {
   context.setConfigurationData(CONFIGURED_LINTS_KEY, lints);
 }
 
 /// Implementers contribute lint warnings via the provided error [reporter].
 abstract class Linter {
   /// Used to report lint warnings.
   /// NOTE: this is set by the framework before visit begins.
@@ skipping 11 matching lines @@
 /// Manages lint timing.
 class LintRegistry {
   /// Dictionary mapping lints (by name) to timers.
   final Map<String, Stopwatch> timers = new HashMap<String, Stopwatch>();
 
   /// Get a timer associated with the given lint rule (or create one if none
   /// exists).
   Stopwatch getTimer(Linter linter) =>
       timers.putIfAbsent(linter.name, () => new Stopwatch());
 }