cleanup errors and fix a couple field negative tests

frog/member.dart

Index: frog/member.dart
diff --git a/frog/member.dart b/frog/member.dart
index a01df90b4c633e2b1e0db1d2698c3a3d51850ac3..5865e200c06dcc7923cce43b33196b42944391f5 100644
--- a/frog/member.dart
+++ b/frog/member.dart
@@ -295,6 +295,10 @@ class FieldMember extends Member {
         definition.type.span);
     }
 
+    if (isStatic && isFinal && value == null) {
+      world.error('static final field is missing initializer', span);
+    }
+
     library._addMember(this);
   }
 
@@ -1242,6 +1246,9 @@ class MemberSet {
 
   void add(Member member) => members.add(member);
 
+  // TODO(jimhug): Always false, or is this needed?
+  bool get isStatic() => members.length == 1 && members[0].isStatic;
+
   bool canInvoke(MethodGenerator context, Arguments args) =>
     members.some((m) => m.canInvoke(context, args));