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

test/cctest/cctest.status

 # Copyright 2011 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 112 matching lines @@
   'test-cpu-profiler/DeoptUntrackedFunction': [PASS, NO_VARIANTS],
 
   ############################################################################
   # Slow tests.
   'test-api/Threading1': [PASS, ['mode == debug', SLOW]],
   'test-api/Threading2': [PASS, ['mode == debug', SLOW]],
   'test-api/Threading3': [PASS, ['mode == debug', SLOW]],
   'test-api/Threading4': [PASS, ['mode == debug', SLOW]],
   'test-debug/CallFunctionInDebugger': [PASS, ['mode == debug', SLOW]],
   'test-strings/StringOOM*': [PASS, ['mode == debug', SKIP]],
+  'test-serialize/CustomSnapshotDataBlobImmortalImmovableRoots': [PASS, ['mode == debug', SKIP]],
 }],  # ALWAYS
 
 ##############################################################################
 ['arch == arm64', {
 
   'test-cpu-profiler/CollectDeoptEvents': [PASS, FAIL],
 
   'test-api/Bug618': [PASS],
 
   # BUG(v8:3385).
@@ skipping 387 matching lines @@
   # TODO(mythria,4680): Incorrect column number on eval.
   'test-api/PromiseRejectCallback': [FAIL],
 }],  # ignition == True
 
 ['ignition == True and msan', {
   # TODO(rmcilroy,4680): Uninitialized memory.
   'test-debug/*': [SKIP],
 }],  # ignition == True and msan
 
 ]