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 e8473d42bec8a4cafb253b4aff776fabf5026a65..cda311664c727940677c919fd2297c15956bb46b 100644
--- a/third_party/WebKit/Source/platform/heap/HeapPage.h
+++ b/third_party/WebKit/Source/platform/heap/HeapPage.h
@@ -782,6 +782,11 @@ public:
     bool shrinkObject(HeapObjectHeader*, size_t);
     void decreasePromptlyFreedSize(size_t size) { m_promptlyFreedSize -= size; }
 
+    bool isObjectAllocatedAtAllocationPoint(HeapObjectHeader* header)
+    {
+        return header->payloadEnd() == m_currentAllocationPoint;
+    }
+
 private:
     void allocatePage();
     Address lazySweepPages(size_t, size_t gcInfoIndex) override;