[turbofan] Fix inlining with --trace-turbo flag.

This makes sure that --trace-turbo or --turbo-source-positions does not
completely disable inlining. The recent introduction of a finalization
interface to the reducer borked the SourcePositionWrapper reducer.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/1406113008

Cr-Commit-Position: refs/heads/master@{#31893}

src/compiler/pipeline.cc

@@ -393,6 +393,8 @@ class SourcePositionWrapper final : public Reducer {
     return reducer_->Reduce(node);
   }
 
+  void Finalize() final { reducer_->Finalize(); }
+
  private:
   Reducer* const reducer_;
   SourcePositionTable* const table_;