Extract DartTypeVisitor and subclasses from resolution_types.

tests/compiler/dart2js/memory_compiler.dart

Index: tests/compiler/dart2js/memory_compiler.dart
diff --git a/tests/compiler/dart2js/memory_compiler.dart b/tests/compiler/dart2js/memory_compiler.dart
index 809dc999ee27f454db916daa4077f3a0c1500fdd..a33e77f01b841502b1e4f024b6b6d08078a492aa 100644
--- a/tests/compiler/dart2js/memory_compiler.dart
+++ b/tests/compiler/dart2js/memory_compiler.dart
@@ -17,6 +17,7 @@ import 'package:compiler/compiler_new.dart'
 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;
@@ -169,7 +170,8 @@ CompilerImpl compilerFor(
           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) {