Add a PLACEHOLDER code kind.

src/snapshot/serialize.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/snapshot/serialize.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/platform/platform.h"
 #include "src/bootstrapper.h"
@@ skipping 2460 matching lines @@
         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::GetSharedFunctionInfo.
         if (code_object != main_code_ && !FLAG_serialize_inner) {
           SerializeBuiltin(Builtins::kCompileLazy, how_to_code, where_to_point);
         } else {
           SerializeGeneric(code_object, how_to_code, where_to_point);
         }
         return;
+      case Code::PLACEHOLDER:
+        UNREACHABLE();
     }
     UNREACHABLE();
   }
 
   // Past this point we should not see any (context-specific) maps anymore.
   CHECK(!obj->IsMap());
   // There should be no references to the global object embedded.
   CHECK(!obj->IsJSGlobalProxy() && !obj->IsGlobalObject());
   // There should be no hash table embedded. They would require rehashing.
   CHECK(!obj->IsHashTable());
@@ skipping 385 matching lines @@
   SerializedCodeData* scd = new SerializedCodeData(cached_data);
   SanityCheckResult r = scd->SanityCheck(isolate, source);
   if (r == CHECK_SUCCESS) return scd;
   cached_data->Reject();
   source->GetIsolate()->counters()->code_cache_reject_reason()->AddSample(r);
   delete scd;
   return NULL;
 }
 }  // namespace internal
 }  // namespace v8