Back off normalizing on set length in sync with adding a property

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 2e5262dabba705325091588e296f3af882736c5d..d6aab60ac4c81943d9a9bf0ca92d6706f1b349d2 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -11786,7 +11786,7 @@ static bool GetOldValue(Isolate* isolate,
 void JSArray::SetLength(Handle<JSArray> array, uint32_t new_length) {
   // We should never end in here with a pixel or external array.
   DCHECK(array->AllowsSetLength());
-  if (JSArray::SetLengthWouldNormalize(array->GetHeap(), new_length)) {
+  if (array->SetLengthWouldNormalize(new_length)) {
     JSObject::NormalizeElements(array);
   }
   array->GetElementsAccessor()->SetLength(array, new_length);
@@ -12519,6 +12519,16 @@ MaybeHandle<Object> JSObject::AddDataElement(Handle<JSObject> object,
 }
 
 
+bool JSArray::SetLengthWouldNormalize(uint32_t new_length) {
+  if (!HasFastElements()) return false;
+  uint32_t capacity = static_cast<uint32_t>(elements()->length());
+  uint32_t new_capacity;
+  return JSArray::SetLengthWouldNormalize(GetHeap(), new_length) &&
+         ShouldConvertToSlowElements(this, capacity, new_length - 1,
+                                     &new_capacity);
+}
+
+
 const double AllocationSite::kPretenureRatio = 0.85;