Empty Array prototype elements protection needs to alert on length change.

test/cctest/test-api.cc

Index: test/cctest/test-api.cc
diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index 7954598c60b14782bb45bd3ffb805b8c284e5c35..32420d1fa4507bc1413ee425df2dde84cc3ff5f1 100644
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -16684,6 +16684,8 @@ TEST(VerifyArrayPrototypeGuarantees) {
   BreakArrayGuarantees("Object.prototype[3] = 'three';");
   BreakArrayGuarantees("Array.prototype.push(1);");
   BreakArrayGuarantees("Array.prototype.unshift(1);");
+  // Break fast array hole handling by changing length.
+  BreakArrayGuarantees("Array.prototype.length = 30;");
   // Break fast array hole handling by prototype structure changes.
   BreakArrayGuarantees("[].__proto__.__proto__ = { funny: true };");
   // By sending elements to dictionary mode.