Do not assign positions to parser-generated desugarings.

src/hydrogen.h

Index: src/hydrogen.h
diff --git a/src/hydrogen.h b/src/hydrogen.h
index f1a6aa1509f04078860bb38ee37e7d3f6da17304..268976af3ddb5416234e77dfe297fadcdfed6c25 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -1868,8 +1868,10 @@ class HGraphBuilder {
 
  protected:
   void SetSourcePosition(int position) {
-    DCHECK(position != RelocInfo::kNoPosition);
-    position_.set_position(position - start_position_);
+    if (position != RelocInfo::kNoPosition) {
+      position_.set_position(position - start_position_);
+    }
+    // Otherwise position remains unknown.
   }
 
   void EnterInlinedSource(int start_position, int id) {