Make setting length on arrays faster.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 452705744a66e51d43d040731cb7cb6ea8da174c..d6b1cb5bbd9975352c519c25bc2896c69c20e7cb 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -5278,7 +5278,7 @@ static Object* ArrayLengthRangeError() {
 
 Object* JSObject::SetElementsLength(Object* len) {
   // We should never end in here with a pixel or external array.
-  ASSERT(!HasPixelElements() && !HasExternalArrayElements());
+  ASSERT(AllowsSetElementsLength());
 
   Object* smi_length = len->ToSmi();
   if (smi_length->IsSmi()) {