Use signaling NaN for holes in fixed double arrays.

test/cctest/test-serialize.cc

 // Copyright 2007-2010 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 70 matching lines @@
   CHECK_EQ(make_code(UNCLASSIFIED, 3),
            encoder.Encode(real_stack_limit_address.address()));
   CHECK_EQ(make_code(UNCLASSIFIED, 8),
            encoder.Encode(ExternalReference::debug_break(isolate).address()));
   CHECK_EQ(
       make_code(UNCLASSIFIED, 4),
       encoder.Encode(ExternalReference::new_space_start(isolate).address()));
   CHECK_EQ(
       make_code(UNCLASSIFIED, 1),
       encoder.Encode(ExternalReference::roots_array_start(isolate).address()));
-  CHECK_EQ(make_code(UNCLASSIFIED, 34),
+  CHECK_EQ(make_code(UNCLASSIFIED, 33),
            encoder.Encode(ExternalReference::cpu_features().address()));
 }
 
 
 TEST(ExternalReferenceDecoder) {
   Isolate* isolate = CcTest::i_isolate();
   v8::V8::Initialize();
 
   ExternalReferenceDecoder decoder(isolate);
   CHECK_EQ(AddressOf(Builtins::kArrayCode),
@@ skipping 1258 matching lines @@
     {
       DisallowCompilation no_compile(reinterpret_cast<Isolate*>(isolate2));
       script = v8::ScriptCompiler::CompileUnbound(
           isolate2, &source, v8::ScriptCompiler::kConsumeCodeCache);
     }
     v8::Local<v8::Value> result = script->BindToCurrentContext()->Run();
     CHECK(result->ToString(isolate2)->Equals(v8_str("XY")));
   }
   isolate2->Dispose();
 }