[serializer] ensure that immortal immovable roots are correctly deserialized.

src/snapshot/startup-serializer.h

Index: src/snapshot/startup-serializer.h
diff --git a/src/snapshot/startup-serializer.h b/src/snapshot/startup-serializer.h
index 1fe22543f474af24c103e74d53ee8b99ffa947a3..71b8475469a7aaafffb8009969daf9f036c38d46 100644
--- a/src/snapshot/startup-serializer.h
+++ b/src/snapshot/startup-serializer.h
@@ -5,6 +5,7 @@
 #ifndef V8_SNAPSHOT_STARTUP_SERIALIZER_H_
 #define V8_SNAPSHOT_STARTUP_SERIALIZER_H_
 
+#include <bitset>
 #include "src/snapshot/serializer.h"
 
 namespace v8 {
@@ -20,9 +21,10 @@ class StartupSerializer : public Serializer {
   ~StartupSerializer() override;
 
   // Serialize the current state of the heap.  The order is:
-  // 1) Strong references.
-  // 2) Partial snapshot cache.
-  // 3) Weak references (e.g. the string table).
+  // 1) Immortal immovable roots
+  // 2) Remaining strong references.
+  // 3) Partial snapshot cache.
+  // 4) Weak references (e.g. the string table).
   void SerializeStrongReferences();
   void SerializeWeakReferencesAndDeferred();
 
@@ -34,9 +36,16 @@ class StartupSerializer : public Serializer {
                        WhereToPoint where_to_point, int skip) override;
   void Synchronize(VisitorSynchronization::SyncTag tag) override;
 
-  intptr_t root_index_wave_front_;
-  bool serializing_builtins_;
+  // Some roots should not be serialized, because their actual value depends on
+  // absolute addresses and they are reset after deserialization, anyway.
+  // In the first pass over the root list, we only serialize immortal immovable
+  // roots. In the second pass, we serialize the rest.
+  bool RootShouldBeSkipped(int root_index);
+
   FunctionCodeHandling function_code_handling_;
+  bool serializing_builtins_;
+  bool serializing_immortal_immovables_roots_;
+  std::bitset<Heap::kStrongRootListLength> root_has_been_serialized_;
   DISALLOW_COPY_AND_ASSIGN(StartupSerializer);
 };