Introduce a handlified version of source position iterator.

src/compiler/bytecode-graph-builder.cc

Index: src/compiler/bytecode-graph-builder.cc
diff --git a/src/compiler/bytecode-graph-builder.cc b/src/compiler/bytecode-graph-builder.cc
index 3dd06c729e0eddc955ffd7cb8028aabcd9838ee2..3788df5b4771fa919da979ab1313990f6a448ec5 100644
--- a/src/compiler/bytecode-graph-builder.cc
+++ b/src/compiler/bytecode-graph-builder.cc
@@ -612,7 +612,7 @@ void BytecodeGraphBuilder::VisitBytecodes(bool stack_check) {
   interpreter::BytecodeArrayIterator iterator(bytecode_array());
   set_bytecode_iterator(&iterator);
   SourcePositionTableIterator source_position_iterator(
-      bytecode_array()->SourcePositionTable());
+      handle(bytecode_array()->SourcePositionTable()));
 
   if (FLAG_trace_environment_liveness) {
     OFStream of(stdout);