Make sure builtin functions don't rely on __proto__.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 2ccd923f73be814c66aa714be28ced5bcd291d56..3132716d899371abc71f08112192bd26c14cf94c 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1626,8 +1626,6 @@ void FullCodeGenerator::VisitObjectLiteral(ObjectLiteral* expr) {
           }
           break;
         }
-        // Fall through.
-      case ObjectLiteral::Property::PROTOTYPE:
         __ push(Operand(rsp, 0));  // Duplicate receiver.
         VisitForStackValue(key);
         VisitForStackValue(value);
@@ -1638,6 +1636,15 @@ void FullCodeGenerator::VisitObjectLiteral(ObjectLiteral* expr) {
           __ Drop(3);
         }
         break;
+      case ObjectLiteral::Property::PROTOTYPE:
+        __ push(Operand(rsp, 0));  // Duplicate receiver.
+        VisitForStackValue(value);
+        if (property->emit_store()) {
+          __ CallRuntime(Runtime::kSetPrototype, 2);
+        } else {
+          __ Drop(2);
+        }
+        break;
       case ObjectLiteral::Property::GETTER:
         accessor_table.lookup(key)->second->getter = value;
         break;