Protect SerializedData from copying.

src/snapshot/code-serializer.cc

Index: src/snapshot/code-serializer.cc
diff --git a/src/snapshot/code-serializer.cc b/src/snapshot/code-serializer.cc
index 9cae0318778f7707eddbb14af44723f9bfae9bbb..48813f5c615988fab98f9b6eaa6005962bca6ac3 100644
--- a/src/snapshot/code-serializer.cc
+++ b/src/snapshot/code-serializer.cc
@@ -485,7 +485,7 @@ Vector<const uint32_t> SerializedCodeData::CodeStubKeys() const {
 SerializedCodeData::SerializedCodeData(ScriptData* data)
     : SerializedData(const_cast<byte*>(data->data()), data->length()) {}
 
-const SerializedCodeData SerializedCodeData::FromCachedData(
+SerializedCodeData SerializedCodeData::FromCachedData(
     Isolate* isolate, ScriptData* cached_data, uint32_t expected_source_hash,
     SanityCheckResult* rejection_result) {
   DisallowHeapAllocation no_gc;