Add visual context on tree view

issue8562
review261951002

opportunity.py

@@ -226,6 +226,12 @@ class SaleOpportunity(Workflow, ModelSQL, ModelView):
         if len(payment_terms) == 1:
             return payment_terms[0].id
 
+    @classmethod
+    def view_attributes(cls):
+        return [
+            ('/tree', 'visual', If(Eval('state') == 'cancelled', 'muted', '')),
+            ]
+
     @classmethod
     def create(cls, vlist):
         pool = Pool()