Faster moving FixedArray elements around.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 861adbc0a688d5db2c1f5d61f52b6141ed53fd2c..d7770a73a3545f40b735d72363f28dd00338f323 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -1230,6 +1230,17 @@ static Object* Runtime_RegExpExec(Arguments args) {
 }
 
 
+static Object* Runtime_FinishArrayPrototypeSetup(Arguments args) {
+  HandleScope scope;
+  ASSERT(args.length() == 1);
+  CONVERT_ARG_CHECKED(JSArray, prototype, 0);
+  // This is necessary to enable fast checks for absence of elements
+  // on Array.prototype and below.
+  prototype->set_elements(Heap::empty_fixed_array());
+  return Smi::FromInt(0);
+}
+
+
 static Object* Runtime_MaterializeRegExpLiteral(Arguments args) {
   HandleScope scope;
   ASSERT(args.length() == 4);