Add last OS error into heap stats.

src/heap.h

 // Copyright 2006-2008 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 1327 matching lines @@
   int* lo_space_size;                   // 13
   int* global_handle_count;             // 14
   int* weak_global_handle_count;        // 15
   int* pending_global_handle_count;     // 16
   int* near_death_global_handle_count;  // 17
   int* destroyed_global_handle_count;   // 18
   int* memory_allocator_size;           // 19
   int* memory_allocator_capacity;       // 20
   int* objects_per_type;                // 21
   int* size_per_type;                   // 22
-  int* end_marker;                      // 23
+  int* os_error;                        // 23
+  int* end_marker;                      // 24
 };
 
 
 class AlwaysAllocateScope {
  public:
   AlwaysAllocateScope() {
     // We shouldn't hit any nested scopes, because that requires
     // non-handle code to call handle code. The code still works but
     // performance will degrade, so we want to catch this situation
     // in debug mode.
@@ skipping 619 matching lines @@
 
   // To speed up scavenge collections new space string are kept
   // separate from old space strings.
   static List<Object*> new_space_strings_;
   static List<Object*> old_space_strings_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_