[interpreter] Minor clean-up of BytecodeSourceInfo.

src/interpreter/bytecode-register-optimizer.cc

Index: src/interpreter/bytecode-register-optimizer.cc
diff --git a/src/interpreter/bytecode-register-optimizer.cc b/src/interpreter/bytecode-register-optimizer.cc
index a30cb26f434ff361b98ea5512810a2facb62f920..ab25f959e48564d823c36161256cb71e70c62b34 100644
--- a/src/interpreter/bytecode-register-optimizer.cc
+++ b/src/interpreter/bytecode-register-optimizer.cc
@@ -312,7 +312,9 @@ void BytecodeRegisterOptimizer::WriteToNextStage(BytecodeNode* node) const {
 
 void BytecodeRegisterOptimizer::WriteToNextStage(
     BytecodeNode* node, const BytecodeSourceInfo& source_info) const {
-  node->source_info().Update(source_info);
+  if (source_info.is_valid()) {
+    node->source_info().Clone(source_info);
+  }
   next_stage_->Write(node);
 }
 
@@ -414,8 +416,9 @@ void BytecodeRegisterOptimizer::RegisterTransfer(
 
 void BytecodeRegisterOptimizer::EmitNopForSourceInfo(
     const BytecodeSourceInfo& source_info) const {
+  DCHECK(source_info.is_valid());
   BytecodeNode nop(Bytecode::kNop);
-  nop.source_info().Update(source_info);
+  nop.source_info().Clone(source_info);
   WriteToNextStage(&nop);
 }