Replaced different means of zone pooling/reusing by one zone segment pool

src/compiler/zone-pool.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_ZONE_POOL_H_
-#define V8_COMPILER_ZONE_POOL_H_
-
-#include <map>
-#include <set>
-#include <vector>
-
-#include "src/zone/zone.h"
-
-namespace v8 {
-namespace internal {
-namespace compiler {
-
-class ZonePool final {
- public:
-  class Scope final {
-   public:
-    explicit Scope(ZonePool* zone_pool)
-        : zone_pool_(zone_pool), zone_(nullptr) {}
-    ~Scope() { Destroy(); }
-
-    Zone* zone() {
-      if (zone_ == nullptr) zone_ = zone_pool_->NewEmptyZone();
-      return zone_;
-    }
-    void Destroy() {
-      if (zone_ != nullptr) zone_pool_->ReturnZone(zone_);
-      zone_ = nullptr;
-    }
-
-   private:
-    ZonePool* const zone_pool_;
-    Zone* zone_;
-    DISALLOW_COPY_AND_ASSIGN(Scope);
-  };
-
-  class StatsScope final {
-   public:
-    explicit StatsScope(ZonePool* zone_pool);
-    ~StatsScope();
-
-    size_t GetMaxAllocatedBytes();
-    size_t GetCurrentAllocatedBytes();
-    size_t GetTotalAllocatedBytes();
-
-   private:
-    friend class ZonePool;
-    void ZoneReturned(Zone* zone);
-
-    typedef std::map<Zone*, size_t> InitialValues;
-
-    ZonePool* const zone_pool_;
-    InitialValues initial_values_;
-    size_t total_allocated_bytes_at_start_;
-    size_t max_allocated_bytes_;
-
-    DISALLOW_COPY_AND_ASSIGN(StatsScope);
-  };
-
-  explicit ZonePool(AccountingAllocator* allocator);
-  ~ZonePool();
-
-  size_t GetMaxAllocatedBytes();
-  size_t GetTotalAllocatedBytes();
-  size_t GetCurrentAllocatedBytes();
-
- private:
-  Zone* NewEmptyZone();
-  void ReturnZone(Zone* zone);
-
-  static const size_t kMaxUnusedSize = 3;
-  typedef std::vector<Zone*> Unused;
-  typedef std::vector<Zone*> Used;
-  typedef std::vector<StatsScope*> Stats;
-
-  Unused unused_;
-  Used used_;
-  Stats stats_;
-  size_t max_allocated_bytes_;
-  size_t total_deleted_bytes_;
-  AccountingAllocator* allocator_;
-
-  DISALLOW_COPY_AND_ASSIGN(ZonePool);
-};
-
-}  // namespace compiler
-}  // namespace internal
-}  // namespace v8
-
-#endif