[turbofan] Implement OSR for outer loops.

src/compiler/frame.h

Index: src/compiler/frame.h
diff --git a/src/compiler/frame.h b/src/compiler/frame.h
index f99d7bd1e11885b0487595449b76d5e6b50f86ec..416d6eea59fda4d16357062ead22c3058afcef54 100644
--- a/src/compiler/frame.h
+++ b/src/compiler/frame.h
@@ -63,6 +63,11 @@ class Frame : public ZoneObject {
     return spill_slot_count_++;
   }
 
+  void ReserveSpillSlots(size_t slot_count) {
+    DCHECK_EQ(0, spill_slot_count_);  // can only reserve before allocation.
+    spill_slot_count_ = static_cast<int>(slot_count);
+  }
+
  private:
   int register_save_area_size_;
   int spill_slot_count_;