[turbofan] Avoid unnecessary copying of nodes during inlining.

src/compiler/js-inlining.h

Index: src/compiler/js-inlining.h
diff --git a/src/compiler/js-inlining.h b/src/compiler/js-inlining.h
index d0ab7c0583379d255526e745a4cf5032e2c16188..88cbf89128089a203651c0da3424fba386b67ae4 100644
--- a/src/compiler/js-inlining.h
+++ b/src/compiler/js-inlining.h
@@ -36,9 +36,12 @@ class JSInliner final : public AdvancedReducer {
   Reduction ReduceJSCall(Node* node, Handle<JSFunction> function);
 
  private:
-  Zone* local_zone_;
+  Graph* graph() const;
+  JSGraph* jsgraph() const { return jsgraph_; }
+
+  Zone* const local_zone_;
   CompilationInfo* info_;
-  JSGraph* jsgraph_;
+  JSGraph* const jsgraph_;
 
   Node* CreateArtificialFrameState(Node* node, Node* outer_frame_state,
                                    int parameter_count,