Revert "Remove failure tag.".

src/spaces.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_SPACES_H_
 #define V8_SPACES_H_
 
 #include "src/allocation.h"
 #include "src/base/atomicops.h"
 #include "src/base/platform/mutex.h"
@@ skipping 294 matching lines @@
 
   void set_next_chunk(MemoryChunk* next) {
     base::Release_Store(&next_chunk_, reinterpret_cast<base::AtomicWord>(next));
   }
 
   void set_prev_chunk(MemoryChunk* prev) {
     base::Release_Store(&prev_chunk_, reinterpret_cast<base::AtomicWord>(prev));
   }
 
   Space* owner() const {
-    return owner_;
+    if ((reinterpret_cast<intptr_t>(owner_) & kFailureTagMask) ==
+        kFailureTag) {
+      return reinterpret_cast<Space*>(reinterpret_cast<intptr_t>(owner_) -
+                                      kFailureTag);
+    } else {
+      return NULL;
+    }
   }
 
   void set_owner(Space* space) {
-    owner_ = space;
+    ASSERT((reinterpret_cast<intptr_t>(space) & kFailureTagMask) == 0);
+    owner_ = reinterpret_cast<Address>(space) + kFailureTag;
+    ASSERT((reinterpret_cast<intptr_t>(owner_) & kFailureTagMask) ==
+           kFailureTag);
   }
 
   base::VirtualMemory* reserved_memory() {
     return &reservation_;
   }
 
   void InitializeReservedMemory() {
     reservation_.Reset();
   }
 
@@ skipping 345 matching lines @@
  protected:
   size_t size_;
   intptr_t flags_;
 
   // Start and end of allocatable memory on this chunk.
   Address area_start_;
   Address area_end_;
 
   // If the chunk needs to remember its memory reservation, it is stored here.
   base::VirtualMemory reservation_;
-  Space* owner_;
+  // The identity of the owning space.  This is tagged as a failure pointer, but
+  // no failure can be in an object, so this can be distinguished from any entry
+  // in a fixed array.
+  Address owner_;
   Heap* heap_;
   // Used by the store buffer to keep track of which pages to mark scan-on-
   // scavenge.
   int store_buffer_counter_;
   // Count of bytes marked black on page.
   int live_byte_count_;
   SlotsBuffer* slots_buffer_;
   SkipList* skip_list_;
   intptr_t write_barrier_counter_;
   // Used by the incremental marker to keep track of the scanning progress in
@@ skipping 2318 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_