Refactor DartTypeVisitor and ElementVisitor.

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 58904818d0e55005fe7d326daa411b915fa5e338..37b1b2314a6f8381aab4edde1d4a2ca2efeb3ab4 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -6894,9 +6894,7 @@ class TypeBuilder implements DartTypeVisitor<dynamic, SsaBuilder> {
 
   TypeBuilder(this.classWorld);
 
-  void visitType(DartType type, _) {
-    throw 'Internal error $type';
-  }
+  void visit(DartType type, SsaBuilder builder) => type.accept(this, builder);
 
   void visitVoidType(VoidType type, SsaBuilder builder) {
     ClassElement cls = builder.backend.findHelper('VoidRuntimeType');
@@ -6956,10 +6954,6 @@ class TypeBuilder implements DartTypeVisitor<dynamic, SsaBuilder> {
     throw 'not implemented visitStatementType($type)';
   }
 
-  void visitGenericType(GenericType type, SsaBuilder builder) {
-    throw 'not implemented visitGenericType($type)';
-  }
-
   void visitInterfaceType(InterfaceType type, SsaBuilder builder) {
     List<HInstruction> inputs = <HInstruction>[];
     for (DartType typeArgument in type.typeArguments) {