- Make array immutable first, then canonicalize it.

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 41861)
+++ runtime/vm/parser.cc	(working copy)
@@ -10784,8 +10784,8 @@
       }
       const_list.SetAt(i, elem->AsLiteralNode()->literal());
     }
+    const_list.MakeImmutable();
     const_list ^= TryCanonicalize(const_list, literal_pos);
-    const_list.MakeImmutable();
     return new(I) LiteralNode(literal_pos, const_list);
   } else {
     // Factory call at runtime.
@@ -11009,8 +11009,8 @@
       }
       key_value_array.SetAt(i, arg->AsLiteralNode()->literal());
     }
+    key_value_array.MakeImmutable();
     key_value_array ^= TryCanonicalize(key_value_array, TokenPos());
-    key_value_array.MakeImmutable();
 
     // Construct the map object.
     const Class& immutable_map_class = Class::Handle(I,