[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/loop-variable-optimizer.h

Index: src/compiler/loop-variable-optimizer.h
diff --git a/src/compiler/loop-variable-optimizer.h b/src/compiler/loop-variable-optimizer.h
index 0dfa8050fec8a81c8ef617a94642b1d36d9f3910..6eff453f09a398f78ad01ce1f6c069810afbe65d 100644
--- a/src/compiler/loop-variable-optimizer.h
+++ b/src/compiler/loop-variable-optimizer.h
@@ -68,7 +68,7 @@ class LoopVariableOptimizer {
   }
 
   void ChangeToInductionVariablePhis();
-  void ChangeFromInductionVariablePhis();
+  void ChangeToPhisAndInsertSigmas();
 
  private:
   const int kAssumedLoopEntryIndex = 0;