Rename failure tag to page owner tag and add proper description.

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 {
-    if ((reinterpret_cast<intptr_t>(owner_) & kFailureTagMask) ==
-        kFailureTag) {
+    if ((reinterpret_cast<intptr_t>(owner_) & kPageHeaderTagMask) ==
+        kPageHeaderTag) {
       return reinterpret_cast<Space*>(reinterpret_cast<intptr_t>(owner_) -
-                                      kFailureTag);
+                                      kPageHeaderTag);
     } else {
       return NULL;
     }
   }
 
   void set_owner(Space* space) {
-    ASSERT((reinterpret_cast<intptr_t>(space) & kFailureTagMask) == 0);
-    owner_ = reinterpret_cast<Address>(space) + kFailureTag;
-    ASSERT((reinterpret_cast<intptr_t>(owner_) & kFailureTagMask) ==
-           kFailureTag);
+    ASSERT((reinterpret_cast<intptr_t>(space) & kPageHeaderTagMask) == 0);
+    owner_ = reinterpret_cast<Address>(space) + kPageHeaderTag;
+    ASSERT((reinterpret_cast<intptr_t>(owner_) & kPageHeaderTagMask) ==
+           kPageHeaderTag);
   }
 
   base::VirtualMemory* reserved_memory() {
     return &reservation_;
   }
 
   void InitializeReservedMemory() {
     reservation_.Reset();
   }
 
@@ skipping 2688 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_