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

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

Index: third_party/WebKit/Source/platform/heap/HeapPage.h
diff --git a/third_party/WebKit/Source/platform/heap/HeapPage.h b/third_party/WebKit/Source/platform/heap/HeapPage.h
index 29ddbd30b920177c197d146af401b1168bee170d..81e8084bf4fe493280d6df6901e4251067de3402 100644
--- a/third_party/WebKit/Source/platform/heap/HeapPage.h
+++ b/third_party/WebKit/Source/platform/heap/HeapPage.h
@@ -781,6 +781,11 @@ public:
     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;