Fix memory leaks in ~Zone and ~Isolate

src/zone.h

 // Copyright 2011 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 47 matching lines @@
 
 class Zone {
  public:
   // Allocate 'size' bytes of memory in the Zone; expands the Zone by
   // allocating new segments of memory on demand using malloc().
   inline void* New(int size);
 
   template <typename T>
   inline T* NewArray(int length);
 
-  // Delete all objects and free all memory allocated in the Zone.
+  // Deletes all objects and free all memory allocated in the Zone. Keeps one
+  // small (size <= kMaximumKeptSegmentSize) segment around if it finds one.
   void DeleteAll();
 
+  // Deletes the last small segment kept around by DeleteAll().
+  void DeleteKeptSegment();
+
   // Returns true if more memory has been allocated in zones than
   // the limit allows.
   inline bool excess_allocation();
 
   inline void adjust_segment_bytes_allocated(int delta);
 
   inline Isolate* isolate() { return isolate_; }
 
   static unsigned allocation_size_;
 
@@ skipping 152 matching lines @@
  public:
   ZoneSplayTree()
       : SplayTree<Config, ZoneListAllocationPolicy>() {}
   ~ZoneSplayTree();
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ZONE_H_