Enable snapshots on MIPS. This is based on

src/serialize.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 467 matching lines @@
   // going on.
   static void TooLateToEnableNow() { too_late_to_enable_now_ = true; }
   static bool enabled() { return serialization_enabled_; }
   SerializationAddressMapper* address_mapper() { return &address_mapper_; }
   void PutRoot(
       int index, HeapObject* object, HowToCode how, WhereToPoint where);
 
  protected:
   static const int kInvalidRootIndex = -1;
 
-  int RootIndex(HeapObject* heap_object);
+  int RootIndex(HeapObject* heap_object, HowToCode from);
   virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) = 0;
   intptr_t root_index_wave_front() { return root_index_wave_front_; }
   void set_root_index_wave_front(intptr_t value) {
     ASSERT(value >= root_index_wave_front_);
     root_index_wave_front_ = value;
   }
 
   class ObjectSerializer : public ObjectVisitor {
    public:
     ObjectSerializer(Serializer* serializer,
@@ skipping 144 matching lines @@
  private:
   virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) {
     return false;
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SERIALIZE_H_