Oilpan: Remove duplicated code between HeapPage and LargeObject

Source/platform/heap/ThreadState.h

Index: Source/platform/heap/ThreadState.h
diff --git a/Source/platform/heap/ThreadState.h b/Source/platform/heap/ThreadState.h
index d8478d3dea7187433cc28cb9e5543a4834f6c5a1..0825f82c515f409ba219e7167f85edc5e1bee1fc 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -49,7 +49,6 @@ class Isolate;
 
 namespace blink {
 
-class BaseHeap;
 class BaseHeapPage;
 class CallbackStack;
 struct GCInfo;
@@ -185,6 +184,7 @@ enum TypedHeaps {
     InlineVectorBackingHeap,
     HashTableBackingHeap,
     FOR_EACH_TYPED_HEAP(TypedHeapEnumName)
+    LargeObjectHeap,
     // Values used for iteration of heap segments.
     NumberOfHeaps,
 };
@@ -463,8 +463,8 @@ public:
     //
     // The heap is split into multiple heap parts based on object
     // types. To get the index for a given type, use
-    // HeapTypeTrait<Type>::index.
-    ThreadHeap* heap(int index) const { return m_heaps[index]; }
+    // HeapIndexTrait<Type>::index.
+    ThreadHeap* heap(int heapIndex) const { return m_heaps[heapIndex]; }
 
 #if ENABLE(ASSERT) || ENABLE(GC_PROFILE_MARKING)
     // Infrastructure to determine if an address is within one of the