Get rid of ZoneScope completely.

src/hydrogen-gvn.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 82 matching lines @@
   void ProcessLoopBlock(HBasicBlock* block,
                         HBasicBlock* before_loop,
                         GVNFlagSet loop_kills,
                         GVNFlagSet* accumulated_first_time_depends,
                         GVNFlagSet* accumulated_first_time_changes);
   bool AllowCodeMotion();
   bool ShouldMove(HInstruction* instr, HBasicBlock* loop_header);
 
   HGraph* graph() { return graph_; }
   CompilationInfo* info() { return info_; }
-  Zone* phase_zone() const { return info_->phase_zone(); }
+  Zone* zone() { return &zone_; }
 
   HGraph* graph_;
   CompilationInfo* info_;
   bool removed_side_effects_;
 
-  Zone* phase_zone_;
-  ZoneScope phase_zone_scope_;
+  Zone zone_;
 
   // A map of block IDs to their side effects.
   ZoneList<GVNFlagSet> block_side_effects_;
 
   // A map of loop header block IDs to their loop's side effects.
   ZoneList<GVNFlagSet> loop_side_effects_;
 
   // Used when collecting side effects on paths from dominator to
   // dominated.
   SparseSet visited_on_paths_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_GVN_H_