Reland "Keep a canonical list of shared function infos."

src/snapshot/serialize.cc

Index: src/snapshot/serialize.cc
diff --git a/src/snapshot/serialize.cc b/src/snapshot/serialize.cc
index 7410c3b393c1a931d991f7f0d1304a75e430e022..a8d0f51b92ff4e93958528e6ef15dfb9c0e0e94b 100644
--- a/src/snapshot/serialize.cc
+++ b/src/snapshot/serialize.cc
@@ -1875,6 +1875,10 @@ void Serializer::ObjectSerializer::Serialize() {
     // Clear cached line ends.
     Object* undefined = serializer_->isolate()->heap()->undefined_value();
     Script::cast(object_)->set_line_ends(undefined);
+    Object* shared_list = Script::cast(object_)->shared_function_infos();
+    if (shared_list->IsWeakFixedArray()) {
+      WeakFixedArray::cast(shared_list)->Compact();
+    }
   }
 
   if (object_->IsExternalString()) {
@@ -2295,7 +2299,7 @@ void CodeSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
         DCHECK(code_object->has_reloc_info_for_serialization());
         // Only serialize the code for the toplevel function unless specified
         // by flag. Replace code of inner functions by the lazy compile builtin.
-        // This is safe, as checked in Compiler::BuildFunctionInfo.
+        // This is safe, as checked in Compiler::GetSharedFunctionInfo.
         if (code_object != main_code_ && !FLAG_serialize_inner) {
           SerializeBuiltin(Builtins::kCompileLazy, how_to_code, where_to_point);
         } else {