[Interpreter] Preserve source positions in peephole optimizer.

src/interpreter/bytecode-pipeline.h

Index: src/interpreter/bytecode-pipeline.h
diff --git a/src/interpreter/bytecode-pipeline.h b/src/interpreter/bytecode-pipeline.h
index ade712c92c323db41759cd17766ca7e5bfb5f361..bbbb5e10645fcbf4295b26a650cab411e16c6e63 100644
--- a/src/interpreter/bytecode-pipeline.h
+++ b/src/interpreter/bytecode-pipeline.h
@@ -52,6 +52,7 @@ class BytecodeSourceInfo final {
   }
 
   bool is_statement() const { return is_valid() && is_statement_; }
+  bool is_expression() const { return is_valid() && !is_statement_; }
 
   bool is_valid() const { return source_position_ != kUninitializedPosition; }
   void set_invalid() { source_position_ = kUninitializedPosition; }