Add guard pages in front of platform allocations

src/spaces.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 629 matching lines @@
   void ReportStatistics();
 #endif
 
   // Due to encoding limitation, we can only have 8K chunks.
   static const int kMaxNofChunks = 1 << kPageSizeBits;
   // If a chunk has at least 16 pages, the maximum heap size is about
   // 8K * 8K * 16 = 1G bytes.
 #ifdef V8_TARGET_ARCH_X64
   static const int kPagesPerChunk = 32;
   // On 64 bit the chunk table consists of 4 levels of 4096-entry tables.
-  static const int kPagesPerChunkLog2 = 5;
   static const int kChunkTableLevels = 4;
   static const int kChunkTableBitsPerLevel = 12;
 #else
   static const int kPagesPerChunk = 16;
   // On 32 bit the chunk table consists of 2 levels of 256-entry tables.
-  static const int kPagesPerChunkLog2 = 4;
   static const int kChunkTableLevels = 2;
   static const int kChunkTableBitsPerLevel = 8;
 #endif
 
  private:
   MemoryAllocator();
 
   static const int kChunkSize = kPagesPerChunk * Page::kPageSize;
-  static const int kChunkSizeLog2 = kPagesPerChunkLog2 + kPageSizeBits;
 
   // Maximum space size in bytes.
   intptr_t capacity_;
   // Maximum subset of capacity_ that can be executable
   intptr_t capacity_executable_;
 
   // Allocated space size in bytes.
   intptr_t size_;
 
   // Allocated executable space size in bytes.
@@ skipping 1635 matching lines @@
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_