Revert of Pool implementation for zone segments

src/zone/accounting-allocator.h

Index: src/zone/accounting-allocator.h
diff --git a/src/zone/accounting-allocator.h b/src/zone/accounting-allocator.h
index f0f2cd11737214f8a805f6d28ec11d7eb4ddbb4e..01c38186d6809e44a4f08ebcc287ee1d09dcdc5d 100644
--- a/src/zone/accounting-allocator.h
+++ b/src/zone/accounting-allocator.h
@@ -19,54 +19,18 @@
 
 class AccountingAllocator {
  public:
-  AccountingAllocator();
-  virtual ~AccountingAllocator();
+  AccountingAllocator() = default;
+  virtual ~AccountingAllocator() = default;
 
-  // Gets an empty segment from the pool or creates a new one.
-  virtual Segment* GetSegment(size_t bytes);
-  // Return unneeded segments to either insert them into the pool or release
-  // them if the pool is already full or memory pressure is high.
-  virtual void ReturnSegment(Segment* memory);
+  virtual Segment* AllocateSegment(size_t bytes);
+  virtual void FreeSegment(Segment* memory);
 
   size_t GetCurrentMemoryUsage() const;
   size_t GetMaxMemoryUsage() const;
 
-  size_t GetCurrentPoolSize() const;
-
-  void MemoryPressureNotification(MemoryPressureLevel level);
-
  private:
-  static const uint8_t kMinSegmentSizePower = 13;
-  static const uint8_t kMaxSegmentSizePower = 18;
-  static const uint8_t kMaxSegmentsPerBucket = 5;
-
-  STATIC_ASSERT(kMinSegmentSizePower <= kMaxSegmentSizePower);
-
-  // Allocates a new segment. Returns nullptr on failed allocation.
-  Segment* AllocateSegment(size_t bytes);
-  void FreeSegment(Segment* memory);
-
-  // Returns a segment from the pool of at least the requested size.
-  Segment* GetSegmentFromPool(size_t requested_size);
-  // Trys to add a segment to the pool. Returns false if the pool is full.
-  bool AddSegmentToPool(Segment* segment);
-
-  // Empties the pool and puts all its contents onto the garbage stack.
-  void ClearPool();
-
-  Segment*
-      unused_segments_heads_[1 + kMaxSegmentSizePower - kMinSegmentSizePower];
-
-  size_t unused_segments_sizes[1 + kMaxSegmentSizePower - kMinSegmentSizePower];
-
-  size_t unused_segments_size_ = 0;
-
-  base::Mutex unused_segments_mutex_;
-
   base::AtomicWord current_memory_usage_ = 0;
   base::AtomicWord max_memory_usage_ = 0;
-
-  base::AtomicValue<MemoryPressureLevel> memory_pressure_level_;
 
   DISALLOW_COPY_AND_ASSIGN(AccountingAllocator);
 };