8-byte align zone allocations of objects that may require it.

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 68 matching lines @@
   inline void adjust_segment_bytes_allocated(int delta);
 
   inline Isolate* isolate() { return isolate_; }
 
   static unsigned allocation_size_;
 
  private:
   friend class Isolate;
   friend class ZoneScope;
 
-  // All pointers returned from New() have this alignment.
+  // All pointers returned from New() have this alignment.  In addition, if the
+  // object being allocated has a size that is divisible by 8 then its alignment
+  // will be 8.
   static const int kAlignment = kPointerSize;
 
   // Never allocate segments smaller than this size in bytes.
   static const int kMinimumSegmentSize = 8 * KB;
 
   // Never allocate segments larger than this size in bytes.
   static const int kMaximumSegmentSize = 1 * MB;
 
   // Never keep segments larger than this size in bytes around.
   static const int kMaximumKeptSegmentSize = 64 * KB;
@@ skipping 137 matching lines @@
  public:
   ZoneSplayTree()
       : SplayTree<Config, ZoneListAllocationPolicy>() {}
   ~ZoneSplayTree();
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ZONE_H_