[turbofan] Avoid unnecessary copying of nodes during inlining.

src/compiler/js-inlining.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_JS_INLINING_H_
 #define V8_COMPILER_JS_INLINING_H_
 
 #include "src/compiler/js-graph.h"
 #include "src/compiler/graph-reducer.h"
 
@@ skipping 18 matching lines @@
         jsgraph_(jsgraph) {}
 
   // Reducer interface, eagerly inlines everything.
   Reduction Reduce(Node* node) final;
 
   // Can be used by inlining heuristics or by testing code directly, without
   // using the above generic reducer interface of the inlining machinery.
   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,
                                    FrameStateType frame_state_type,
                                    Handle<SharedFunctionInfo> shared);
 
   Node* CreateTailCallerFrameState(Node* node, Node* outer_frame_state);
 
   Reduction InlineCall(Node* call, Node* new_target, Node* context,
                        Node* frame_state, Node* start, Node* end);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_JS_INLINING_H_