[serializer] checksum a larger part of the code snapshot.

src/snapshot/code-serializer.h

 // Copyright 2016 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.
 
 #ifndef V8_SNAPSHOT_CODE_SERIALIZER_H_
 #define V8_SNAPSHOT_CODE_SERIALIZER_H_
 
 #include "src/parsing/preparse-data.h"
 #include "src/snapshot/serializer.h"
 
@@ skipping 97 matching lines @@
 
   Vector<const uint32_t> CodeStubKeys() const;
 
   static uint32_t SourceHash(Handle<String> source);
 
  private:
   explicit SerializedCodeData(ScriptData* data);
   SerializedCodeData(const byte* data, int size)
       : SerializedData(const_cast<byte*>(data), size) {}
 
+  Vector<const byte> DataWithoutHeader() const {
+    return Vector<const byte>(data_ + kHeaderSize, size_ - kHeaderSize);
+  }
+
   SanityCheckResult SanityCheck(Isolate* isolate,
                                 uint32_t expected_source_hash) const;
   // The data header consists of uint32_t-sized entries:
   // [0] magic number and external reference count
   // [1] version hash
   // [2] source hash
   // [3] cpu features
   // [4] flag hash
   // [5] number of code stub keys
   // [6] number of reservation size entries
@@ skipping 12 matching lines @@
   static const int kPayloadLengthOffset = kNumCodeStubKeysOffset + kInt32Size;
   static const int kChecksum1Offset = kPayloadLengthOffset + kInt32Size;
   static const int kChecksum2Offset = kChecksum1Offset + kInt32Size;
   static const int kHeaderSize = kChecksum2Offset + kInt32Size;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_SNAPSHOT_CODE_SERIALIZER_H_