Extract DartTypeVisitor and subclasses from resolution_types.

tests/compiler/dart2js/memory_compiler.dart

 // Copyright (c) 2016, 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.test.memory_compiler;
 
 import 'dart:async';
 
 import 'package:compiler/compiler.dart' show DiagnosticHandler;
 import 'package:compiler/compiler_new.dart'
     show
         CompilationResult,
         CompilerDiagnostics,
         CompilerOutput,
         Diagnostic,
         PackagesDiscoveryProvider;
 import 'package:compiler/src/diagnostics/messages.dart' show Message;
 import 'package:compiler/src/elements/entities.dart'
     show LibraryEntity, MemberEntity;
+import 'package:compiler/src/elements/resolution_types.dart' show Types;
 import 'package:compiler/src/enqueue.dart' show ResolutionEnqueuer;
 import 'package:compiler/src/null_compiler_output.dart' show NullCompilerOutput;
 import 'package:compiler/src/library_loader.dart' show LoadedLibraries;
 import 'package:compiler/src/options.dart' show CompilerOptions;
 
 import 'memory_source_file_helper.dart';
 
 export 'output_collector.dart';
 export 'package:compiler/compiler_new.dart' show CompilationResult;
 export 'diagnostic_helper.dart';
@@ skipping 132 matching lines @@
           entryPoint: entryPoint,
           resolutionInputs: resolutionInputs,
           libraryRoot: libraryRoot,
           packageRoot: packageRoot,
           options: options,
           environment: {},
           packageConfig: packageConfig,
           packagesDiscoveryProvider: packagesDiscoveryProvider));
 
   if (cachedCompiler != null) {
-    compiler.types = cachedCompiler.types.copy(compiler.resolution);
+    Types types = cachedCompiler.types;
+    compiler.types = types.copy(compiler.resolution);
     Map copiedLibraries = {};
     cachedCompiler.libraryLoader.libraries.forEach((library) {
       if (library.isPlatformLibrary) {
         var libraryLoader = compiler.libraryLoader;
         libraryLoader.mapLibrary(library);
         copiedLibraries[library.canonicalUri] = library;
       }
     });
     compiler.processLoadedLibraries(new MemoryLoadedLibraries(copiedLibraries));
     ResolutionEnqueuer resolutionEnqueuer = compiler.startResolution();
@@ skipping 65 matching lines @@
       handler = (Uri uri, int begin, int end, String message, Diagnostic kind) {
         diagnosticHandler(uri, begin, end, message, kind);
         formattingHandler(uri, begin, end, message, kind);
       };
     }
   } else if (diagnosticHandler == null) {
     handler = (Uri uri, int begin, int end, String message, Diagnostic kind) {};
   }
   return handler;
 }