Oilpan: always shrink tail-allocated backing storage (reland.)

third_party/WebKit/Source/platform/heap/HeapPage.h

 /*
  * Copyright (C) 2013 Google Inc. 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
@@ skipping 763 matching lines @@
     Address allocateObject(size_t allocationSize, size_t gcInfoIndex);
 
     void freePage(NormalPage*);
 
     bool coalesce();
     void promptlyFreeObject(HeapObjectHeader*);
     bool expandObject(HeapObjectHeader*, size_t);
     bool shrinkObject(HeapObjectHeader*, size_t);
     void decreasePromptlyFreedSize(size_t size) { m_promptlyFreedSize -= size; }
 
+    bool isObjectAllocatedLast(HeapObjectHeader* header)
+    {
+        return header->payloadEnd() == m_currentAllocationPoint;
+    }
+
 private:
     void allocatePage();
     Address lazySweepPages(size_t, size_t gcInfoIndex) override;
     Address outOfLineAllocate(size_t allocationSize, size_t gcInfoIndex);
     Address currentAllocationPoint() const { return m_currentAllocationPoint; }
     size_t remainingAllocationSize() const { return m_remainingAllocationSize; }
     bool hasCurrentAllocationArea() const { return currentAllocationPoint() && remainingAllocationSize(); }
     void setAllocationPoint(Address, size_t);
     void updateRemainingAllocationSize();
     Address allocateFromFreeList(size_t, size_t gcInfoIndex);
@@ skipping 148 matching lines @@
         SET_MEMORY_ACCESSIBLE(result, allocationSize - sizeof(HeapObjectHeader));
         ASSERT(findPageFromAddress(headerAddress + allocationSize - 1));
         return result;
     }
     return outOfLineAllocate(allocationSize, gcInfoIndex);
 }
 
 } // namespace blink
 
 #endif // HeapPage_h