Turn zone_excess_limit_ into a constant.

src/zone.h

 // Copyright 2012 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 73 matching lines @@
   // 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;
 
   // Report zone excess when allocation exceeds this limit.
-  int zone_excess_limit_;
+  static const int kExcessLimit = 256 * MB;
 
   // The number of bytes allocated in this zone so far.
   unsigned allocation_size_;
 
   // The number of bytes allocated in segments.  Note that this number
   // includes memory allocated from the OS but not yet allocated from
   // the zone.
   int segment_bytes_allocated_;
 
   // Expand the Zone to hold at least 'size' more bytes and allocate
@@ skipping 117 matching lines @@
       : SplayTree<Config, ZoneAllocationPolicy>(ZoneAllocationPolicy(zone)) {}
   ~ZoneSplayTree();
 };
 
 
 typedef TemplateHashMapImpl<ZoneAllocationPolicy> ZoneHashMap;
 
 } }  // namespace v8::internal
 
 #endif  // V8_ZONE_H_