Improve positions tracking inside the HGraphBuilder.

src/hydrogen-representation-changes.cc

Index: src/hydrogen-representation-changes.cc
diff --git a/src/hydrogen-representation-changes.cc b/src/hydrogen-representation-changes.cc
index 07fc8be38c0437951b05ea4210db9e5b196f1d0a..7d0720c6044d0d83dba8a61f867016e726a57128 100644
--- a/src/hydrogen-representation-changes.cc
+++ b/src/hydrogen-representation-changes.cc
@@ -61,10 +61,11 @@ void HRepresentationChangesPhase::InsertRepresentationChangeForUse(
   if (new_value == NULL) {
     new_value = new(graph()->zone()) HChange(
         value, to, is_truncating_to_smi, is_truncating_to_int);
-    if (use_value->operand_position(use_index) != RelocInfo::kNoPosition) {
+    if (!use_value->operand_position(use_index).IsUnknown()) {
       new_value->set_position(use_value->operand_position(use_index));
     } else {
-      ASSERT(!FLAG_emit_opt_code_positions || !graph()->info()->IsOptimizing());
+      ASSERT(!FLAG_hydrogen_track_positions ||
+             !graph()->info()->IsOptimizing());
     }
   }