Revert of Serializer: clear string hash for code serializer. (patchset #1 id:1...

Revert of Serializer: clear string hash for code serializer. (patchset #1 id:1 of https://codereview.chromium.org/1183483006/)

Reason for revert:
This led to the roll being stuck: https://codereview.chromium.org/1189863003/

Original issue's description:
> Serializer: clear string hash for code serializer.
>
> R=jochen@chromium.org
> BUG=v8:4179
> LOG=N
>
> Committed: https://crrev.com/a0342678e865337215f9195f983c6013b60e7641
> Cr-Commit-Position: refs/heads/master@{#29016}

TBR=jochen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4179

Review URL: https://codereview.chromium.org/1186173004

Cr-Commit-Position: refs/heads/master@{#29065}

src/snapshot/serialize.cc

@@ -714,16 +714,20 @@ class StringTableInsertionKey : public HashTableKey {
 
 HeapObject* Deserializer::PostProcessNewObject(HeapObject* obj, int space) {
   if (deserializing_user_code()) {
-    if (obj->IsInternalizedString()) {
+    if (obj->IsString()) {
+      String* string = String::cast(obj);
+      // Uninitialize hash field as the hash seed may have changed.
+      string->set_hash_field(String::kEmptyHashField);
+      if (string->IsInternalizedString()) {
         // Canonicalize the internalized string. If it already exists in the
         // string table, set it to forward to the existing one.
         DisallowHeapAllocation no_gc;
-      String* string = String::cast(obj);
         HandleScope scope(isolate_);
         StringTableInsertionKey key(string);
         String* canonical = *StringTable::LookupKey(isolate_, &key);
         string->SetForwardedInternalizedString(canonical);
         return canonical;
+      }
     } else if (obj->IsScript()) {
       // Assign a new script id to avoid collision.
       Script::cast(obj)->set_id(isolate_->heap()->NextScriptId());
@@ -2314,24 +2318,12 @@ void CodeSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
 void CodeSerializer::SerializeGeneric(HeapObject* heap_object,
                                       HowToCode how_to_code,
                                       WhereToPoint where_to_point) {
-  int string_hash = String::kEmptyHashField;
-  if (heap_object->IsString()) {
-    String* string = String::cast(heap_object);
-    if (string->IsInternalizedString()) num_internalized_strings_++;
-    // Temporarily clear string hash.
-    string_hash = string->hash_field();
-    string->set_hash_field(String::kEmptyHashField);
-  }
+  if (heap_object->IsInternalizedString()) num_internalized_strings_++;
 
   // Object has not yet been serialized.  Serialize it here.
   ObjectSerializer serializer(this, heap_object, sink_, how_to_code,
                               where_to_point);
   serializer.Serialize();
-
-  if (string_hash != String::kEmptyHashField) {
-    // Restore string hash.
-    String::cast(heap_object)->set_hash_field(String::kEmptyHashField);
-  }
 }
 
 

src/snapshot/serialize.h

@@ -307,7 +307,7 @@ class SerializerDeserializer: public ObjectVisitor {
 
  protected:
   static bool CanBeDeferred(HeapObject* o) {
-    return !o->IsInternalizedString() && !o->IsScript();
+    return !o->IsString() && !o->IsScript();
   }
 
   // ---------- byte code range 0x00..0x7f ----------