Use proper internal name for implicit static final getters.

runtime/vm/ast.cc

Index: runtime/vm/ast.cc
===================================================================
--- runtime/vm/ast.cc	(revision 25052)
+++ runtime/vm/ast.cc	(working copy)
@@ -495,7 +495,7 @@
     const Function& getter =
         Function::Handle(cls().LookupStaticFunction(getter_name));
     ASSERT(!getter.IsNull() &&
-           (getter.kind() == RawFunction::kConstImplicitGetter));
+           (getter.kind() == RawFunction::kImplicitStaticFinalGetter));
 #endif
     return new StoreStaticFieldNode(token_pos(), field, rhs);
   }