Fix adding to WeakFixedArray after compaction.

src/objects.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <iomanip>
 #include <sstream>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 8292 matching lines @@
 
 void WeakFixedArray::Compact() {
   FixedArray* array = FixedArray::cast(this);
   int new_length = kFirstIndex;
   for (int i = kFirstIndex; i < array->length(); i++) {
     Object* element = array->get(i);
     if (element->IsSmi()) continue;
     if (WeakCell::cast(element)->cleared()) continue;
     array->set(new_length++, element);
   }
+  if (new_length == kFirstIndex) new_length++;
   array->Shrink(new_length);
   set_last_used_index(0);
 }
 
 
 void WeakFixedArray::Remove(Handle<HeapObject> value) {
   // Optimize for the most recently added element to be removed again.
   int first_index = last_used_index();
   for (int i = first_index;;) {
     if (Get(i) == *value) {
@@ skipping 8798 matching lines @@
 void PropertyCell::SetValueWithInvalidation(Handle<PropertyCell> cell,
                                             Handle<Object> new_value) {
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 } }  // namespace v8::internal