Removed funky Maybe constructor and made fields private.

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index d3d40f12f5add8b0c4ab38d2c263a3385f515352..847101480e0cc9b8e2ae1aec5a2cf6b16b17b679 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -2076,8 +2076,8 @@ class BinaryOperation FINAL : public Expression {
     return has_fixed_right_arg_ ? Just(fixed_right_arg_value_) : Nothing<int>();
   }
   void set_fixed_right_arg(Maybe<int> arg) {
-    has_fixed_right_arg_ = arg.has_value;
-    if (arg.has_value) fixed_right_arg_value_ = arg.value;
+    has_fixed_right_arg_ = arg.IsJust();
+    if (arg.IsJust()) fixed_right_arg_value_ = arg.FromJust();
   }
 
   virtual void RecordToBooleanTypeFeedback(