Fix hints reported by analyzer.

pkg/compiler/lib/src/compiler.dart

 // Copyright (c) 2012, 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 dart2js.compiler_base;
 
 import 'dart:async' show EventSink, Future;
 
 import '../compiler_new.dart' as api;
 import 'cache_strategy.dart' show CacheStrategy;
@@ skipping 49 matching lines @@
 import 'parser/parser_task.dart' show ParserTask;
 import 'patch_parser.dart' show PatchParserTask;
 import 'resolution/resolution.dart' show ResolverTask;
 import 'resolved_uri_translator.dart';
 import 'scanner/scanner_task.dart' show ScannerTask;
 import 'script.dart' show Script;
 import 'serialization/task.dart' show SerializationTask;
 import 'ssa/nodes.dart' show HInstruction;
 import 'tokens/token.dart' show StringToken, Token, TokenPair;
 import 'tokens/token_map.dart' show TokenMap;
-import 'tracer.dart' show Tracer;
 import 'tree/tree.dart' show Node, TypeAnnotation;
 import 'typechecker.dart' show TypeCheckerTask;
 import 'types/types.dart' show GlobalTypeInferenceTask;
 import 'universe/selector.dart' show Selector;
 import 'universe/world_builder.dart'
     show ResolutionWorldBuilder, CodegenWorldBuilder;
 import 'universe/use.dart' show StaticUse, TypeUse;
 import 'universe/world_impact.dart'
     show
         ImpactStrategy,
         WorldImpact,
-        WorldImpactBuilder,
         WorldImpactBuilderImpl;
 import 'util/util.dart' show Link, Setlet;
 import 'world.dart' show ClosedWorld, ClosedWorldRefiner, ClosedWorldImpl;
 
 typedef Backend MakeBackendFunction(Compiler compiler);
 
 typedef CompilerDiagnosticReporter MakeReporterFunction(
     Compiler compiler, CompilerOptions options);
 
 abstract class Compiler implements LibraryLoaderListener {
@@ skipping 1180 matching lines @@
   }
 
   ClassElement _mirrorsUsedClass;
   ClassElement get mirrorsUsedClass =>
       _mirrorsUsedClass ??= _findRequired(mirrorsLibrary, 'MirrorsUsed');
 
   bool isMirrorsUsedConstructor(ConstructorElement element) =>
       mirrorsLibrary != null && mirrorsUsedClass == element.enclosingClass;
 
   ConstructorElement _mirrorsUsedConstructor;
-  @override
+
   ConstructorElement get mirrorsUsedConstructor {
     if (_mirrorsUsedConstructor == null) {
       ClassElement cls = mirrorsUsedClass;
       if (cls != null) {
         cls.ensureResolved(resolution);
         _mirrorsUsedConstructor = cls.constructors.head;
       }
     }
     return _mirrorsUsedConstructor;
   }
@@ skipping 657 matching lines @@
   @override
   IdGenerator get idGenerator => _compiler.idGenerator;
 
   @override
   ConstantEnvironment get constants => _compiler.constants;
 
   @override
   MirrorUsageAnalyzerTask get mirrorUsageAnalyzerTask =>
       _compiler.mirrorUsageAnalyzerTask;
 
-  @override
   LibraryElement get coreLibrary => _compiler._commonElements.coreLibrary;
 
   @override
   bool get wasProxyConstantComputedTestingOnly => _proxyConstant != null;
 
   @override
   void registerClass(ClassElement cls) {
     enqueuer.worldBuilder.registerClass(cls);
   }
 
@@ skipping 260 matching lines @@
   _ElementScanner(this.scanner);
   void scanLibrary(LibraryElement library) => scanner.scanLibrary(library);
   void scanUnit(CompilationUnitElement unit) => scanner.scan(unit);
 }
 
 class _EmptyEnvironment implements Environment {
   const _EmptyEnvironment();
 
   String valueOf(String key) => null;
 }