Fix infinite loop when there is a cycle in the class hierarchy (issue 28837)

pkg/analyzer/lib/src/generated/error_verifier.dart

Index: pkg/analyzer/lib/src/generated/error_verifier.dart
diff --git a/pkg/analyzer/lib/src/generated/error_verifier.dart b/pkg/analyzer/lib/src/generated/error_verifier.dart
index c4ebab67fa4fec985c9ba87bdd0f472fc7953221..fe65b45d70304b688b7a85f752ef36e3adf91b0c 100644
--- a/pkg/analyzer/lib/src/generated/error_verifier.dart
+++ b/pkg/analyzer/lib/src/generated/error_verifier.dart
@@ -4908,6 +4908,9 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
   }
 
   void _checkForMustCallSuper(MethodDeclaration node) {
+    if (node.isStatic) {
+      return;
+    }
     MethodElement element = _findOverriddenMemberThatMustCallSuper(node);
     if (element != null) {
       _InvocationCollector collector = new _InvocationCollector();
@@ -6408,7 +6411,8 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
     }
     String name = member.name;
     ClassElement superclass = classElement.supertype?.element;
-    while (superclass != null) {
+    Set<ClassElement> visitedClasses = new Set();

[scheglov, 2017/02/20 18:27:02]

Type argument in creation?

[Brian Wilkerson, 2017/02/20 19:46:30]

Done

+    while (superclass != null && visitedClasses.add(superclass)) {
       ExecutableElement member = superclass.getMethod(name) ??
           superclass.getGetter(name) ??
           superclass.getSetter(name);