[turbofan] Port Crankshaft's weak objects mechanism to TurboFan.

src/crankshaft/lithium.h

 // Copyright 2012 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_CRANKSHAFT_LITHIUM_H_
 #define V8_CRANKSHAFT_LITHIUM_H_
 
 #include <set>
 
 #include "src/allocation.h"
@@ skipping 672 matching lines @@
   BitVector* allocated_double_registers() {
     return allocated_double_registers_;
   }
 
  protected:
   LChunk(CompilationInfo* info, HGraph* graph);
 
   int spill_slot_count_;
 
  private:
-  void RegisterWeakObjectsInOptimizedCode(Handle<Code> code) const;
   void CommitDependencies(Handle<Code> code) const;
 
   CompilationInfo* info_;
   HGraph* const graph_;
   BitVector* allocated_double_registers_;
   ZoneList<LInstruction*> instructions_;
   ZoneList<LPointerMap*> pointer_maps_;
   ZoneList<Handle<SharedFunctionInfo>> inlined_functions_;
   ZoneList<Handle<Map>> deprecation_dependencies_;
   ZoneList<Handle<Map>> stability_dependencies_;
@@ skipping 128 matching lines @@
   InputIterator input_iterator_;
   DeepIterator env_iterator_;
 };
 
 class LInstruction;
 class LCodeGen;
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CRANKSHAFT_LITHIUM_H_