Compact weak fixed arrays before serializing.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index f57c569d09b36bf08bcdab3288dd552b85b960c6..9f2df206d86e2bffb5893c17529187dbfe636371 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -8295,6 +8295,19 @@ Handle<WeakFixedArray> WeakFixedArray::Add(
 }
 
 
+void WeakFixedArray::Compact() {
+  FixedArray* array = FixedArray::cast(this);
+  int w = 0;

[ulan, 2015/04/21 13:42:10]

s/w/new_length/

+  for (int r = 0; r < array->length(); r++) {
+    Object* item = array->get(r);
+    if (item->IsSmi()) continue;
+    if (WeakCell::cast(item)->cleared()) continue;
+    array->set(w++, item);
+  }
+  array->Shrink(w);
+}
+
+
 void WeakFixedArray::Remove(Handle<HeapObject> value) {
   // Optimize for the most recently added element to be removed again.
   int first_index = last_used_index();