Extract DartTypeVisitor and subclasses from resolution_types.

pkg/compiler/lib/src/serialization/equivalence.dart

Index: pkg/compiler/lib/src/serialization/equivalence.dart
diff --git a/pkg/compiler/lib/src/serialization/equivalence.dart b/pkg/compiler/lib/src/serialization/equivalence.dart
index 68075b1a432c4227269f9eb8dda950735cc8c514..54ae164b20fb2a8a6200cd6f60b58315f5a342ff 100644
--- a/pkg/compiler/lib/src/serialization/equivalence.dart
+++ b/pkg/compiler/lib/src/serialization/equivalence.dart
@@ -634,7 +634,8 @@ class ElementIdentityEquivalence extends BaseElementVisitor<bool, Element> {
 }
 
 /// Visitor that checks for equivalence of [ResolutionDartType]s.
-class TypeEquivalence implements DartTypeVisitor<bool, ResolutionDartType> {
+class TypeEquivalence
+    implements ResolutionDartTypeVisitor<bool, ResolutionDartType> {
   final TestStrategy strategy;
 
   const TypeEquivalence([this.strategy = const TestStrategy()]);