Fulfill some code serializer related TODOs.

src/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/v8.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/platform/platform.h"
 #include "src/bootstrapper.h"
@@ skipping 1967 matching lines @@
 }
 
 
 void CodeSerializer::SerializeCodeStub(Code* stub, HowToCode how_to_code,
                                        WhereToPoint where_to_point) {
   DCHECK((how_to_code == kPlain && where_to_point == kStartOfObject) ||
          (how_to_code == kPlain && where_to_point == kInnerPointer) ||
          (how_to_code == kFromCode && where_to_point == kInnerPointer));
   uint32_t stub_key = stub->stub_key();
   DCHECK(CodeStub::MajorKeyFromKey(stub_key) != CodeStub::NoCache);
+  DCHECK(CodeStub::GetCode(isolate(), stub_key)->IsCode());
 
   int index = AddCodeStubKey(stub_key) + kCodeStubsBaseIndex;
 
   if (FLAG_trace_code_serializer) {
     PrintF("Encoding code stub %s as %d\n",
            CodeStub::MajorName(CodeStub::MajorKeyFromKey(stub_key), false),
            index);
   }
 
   sink_->Put(kAttachedReference + how_to_code + where_to_point, "CodeStub");
@@ skipping 110 matching lines @@
 
 int SerializedCodeData::CheckSum(String* string) {
   int checksum = Version::Hash();
 #ifdef DEBUG
   uint32_t seed = static_cast<uint32_t>(checksum);
   checksum = static_cast<int>(IteratingStringHasher::Hash(string, seed));
 #endif  // DEBUG
   return checksum;
 }
 } }  // namespace v8::internal