Ensure slow properties for simple {__proto__:null} literals.

test/mjsunit/object-literal.js

Index: test/mjsunit/object-literal.js
diff --git a/test/mjsunit/object-literal.js b/test/mjsunit/object-literal.js
index 8fdf68d42e1b3e1a5ad8cbb57cfa7c2ccbb022ac..f3727163f6fbcde9469f2ea0b80f40fbaa4f494d 100644
--- a/test/mjsunit/object-literal.js
+++ b/test/mjsunit/object-literal.js
@@ -25,6 +25,8 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+// Flags: --allow-natives-syntax
+
 var obj = {
     a: 7,
     b: { x: 12, y: 24 },
@@ -301,3 +303,50 @@ TestNumericNamesSetter(['1.2', '1.3'], {
   var l = new Proxy({[prop]: 'my value'}, handler);
   assertEquals('my value', l[prop]);
 })();
+
+(function TestLiteralWithNullProto() {
+  // Assume dictionary usage for simple null prototype literal objects,
+  // this is equivalent to Object.create(null).
+  var obj = {__proto__:null};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+  // Once we add inline properties we probably don't want slow properties
+  // anymore.
+  obj = {__proto__:null, a:1, b:2};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {__proto__: null, ["a"]: 1};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {__proto__: null, a: obj};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {a:1, b:2, __proto__:null};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {["a"]: 1, __proto__: null};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {a: obj, __proto__: null};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+})();
+
+(function TestSlowLiteralOptimized() {
+  function f() {
+    return {__proto__:null};
+  }
+  let obj = f();
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  %OptimizeFunctionOnNextCall(f);
+  obj = f();
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+})();