Check for cyclic type variable bounds.

sdk/lib/_internal/compiler/implementation/dart_types.dart

Index: sdk/lib/_internal/compiler/implementation/dart_types.dart
diff --git a/sdk/lib/_internal/compiler/implementation/dart_types.dart b/sdk/lib/_internal/compiler/implementation/dart_types.dart
index 5f00a6239398959059aec7c69a12f529a4a0d9a7..ce0cdfa9e188103f6fd208eafc282bcef89bbd05 100644
--- a/sdk/lib/_internal/compiler/implementation/dart_types.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart_types.dart
@@ -133,6 +133,15 @@ abstract class DartType {
   bool get containsTypeVariables => typeVariableOccurrence != null;
 
   accept(DartTypeVisitor visitor, var argument);
+
+  void visitChildren(DartTypeVisitor visitor, var argument) {}
+
+  static void visitList(Link<DartType> types,
+                        DartTypeVisitor visitor, var argument) {
+    for (Link<DartType> link = types; !link.isEmpty ; link = link.tail) {
+      link.head.accept(visitor, argument);
+    }
+  }
 }
 
 /**
@@ -396,6 +405,10 @@ abstract class GenericType extends DartType {
     return _findTypeVariableOccurrence(typeArguments);
   }
 
+  void visitChildren(DartTypeVisitor visitor, var argument) {
+    DartType.visitList(typeArguments, visitor, argument);
+  }
+
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb.write(name.slowToString());
@@ -663,6 +676,13 @@ class FunctionType extends DartType {
     return visitor.visitFunctionType(this, argument);
   }
 
+  void visitChildren(DartTypeVisitor visitor, var argument) {
+   returnType.accept(visitor, argument);
+   DartType.visitList(parameterTypes, visitor, argument);
+   DartType.visitList(optionalParameterTypes, visitor, argument);
+   DartType.visitList(namedParameterTypes, visitor, argument);
+  }
+
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb.write('(');