Clear recorded slots when creating filler objects.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 3bfe1d1df48a0e0bda80a5d9113e45da92abfb9f..a49bc807f1707ece12e9087c4a1a5b9e71147e74 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -1738,7 +1738,8 @@ bool String::MakeExternal(v8::String::ExternalStringResource* resource) {
 
   // Byte size of the external String object.
   int new_size = this->SizeFromMap(new_map);
-  heap->CreateFillerObjectAt(this->address() + new_size, size - new_size);
+  heap->CreateFillerObjectAt(this->address() + new_size, size - new_size,
+                             ClearRecordedSlots::kNo);
 
   // We are storing the new map using release store after creating a filler for
   // the left-over space to avoid races with the sweeper thread.
@@ -1799,7 +1800,8 @@ bool String::MakeExternal(v8::String::ExternalOneByteStringResource* resource) {
 
   // Byte size of the external String object.
   int new_size = this->SizeFromMap(new_map);
-  heap->CreateFillerObjectAt(this->address() + new_size, size - new_size);
+  heap->CreateFillerObjectAt(this->address() + new_size, size - new_size,
+                             ClearRecordedSlots::kNo);
 
   // We are storing the new map using release store after creating a filler for
   // the left-over space to avoid races with the sweeper thread.
@@ -2943,8 +2945,8 @@ void MigrateFastToFast(Handle<JSObject> object, Handle<Map> new_map) {
 
   if (instance_size_delta > 0) {
     Address address = object->address();
-    heap->CreateFillerObjectAt(
-        address + new_instance_size, instance_size_delta);
+    heap->CreateFillerObjectAt(address + new_instance_size, instance_size_delta,
+                               ClearRecordedSlots::kYes);
     heap->AdjustLiveBytes(*object, -instance_size_delta,
                           Heap::CONCURRENT_TO_SWEEPER);
   }
@@ -3039,7 +3041,7 @@ void MigrateFastToSlow(Handle<JSObject> object, Handle<Map> new_map,
   if (instance_size_delta > 0) {
     Heap* heap = isolate->heap();
     heap->CreateFillerObjectAt(object->address() + new_instance_size,
-                               instance_size_delta);
+                               instance_size_delta, ClearRecordedSlots::kYes);
     heap->AdjustLiveBytes(*object, -instance_size_delta,
                           Heap::CONCURRENT_TO_SWEEPER);
   }
@@ -12115,7 +12117,8 @@ Handle<String> SeqString::Truncate(Handle<SeqString> string, int new_length) {
   Heap* heap = string->GetHeap();
   // Sizes are pointer size aligned, so that we can use filler objects
   // that are a multiple of pointer size.
-  heap->CreateFillerObjectAt(start_of_string + new_size, delta);
+  heap->CreateFillerObjectAt(start_of_string + new_size, delta,
+                             ClearRecordedSlots::kNo);
   heap->AdjustLiveBytes(*string, -delta, Heap::CONCURRENT_TO_SWEEPER);
 
   // We are storing the new length using release store after creating a filler