Move EnsureFastWritableElements into the elements accessor.

src/elements.h

Index: src/elements.h
diff --git a/src/elements.h b/src/elements.h
index 07f24c1f8c6b920a0af93698a40e95b80e2211b3..b2d581edc6703644d9d44957b999e75ca64ce89a 100644
--- a/src/elements.h
+++ b/src/elements.h
@@ -52,11 +52,6 @@ class ElementsAccessor {
     return HasElement(holder, index, handle(holder->elements()), filter);
   }
 
-  // Returns true if the backing store is compact in the given range
-  virtual bool IsPacked(Handle<JSObject> holder,
-                        Handle<FixedArrayBase> backing_store, uint32_t start,
-                        uint32_t end) = 0;
-
   virtual Handle<Object> Get(Handle<JSObject> holder, uint32_t entry) = 0;
 
   virtual PropertyDetails GetDetails(JSObject* holder, uint32_t entry) = 0;
@@ -123,28 +118,22 @@ class ElementsAccessor {
   static Handle<JSArray> Concat(Isolate* isolate, Arguments* args,
                                 uint32_t concat_size);
 
-  virtual uint32_t Push(Handle<JSArray> receiver,
-                        Handle<FixedArrayBase> backing_store, Arguments* args,
+  virtual uint32_t Push(Handle<JSArray> receiver, Arguments* args,
                         uint32_t push_size) = 0;
 
   virtual uint32_t Unshift(Handle<JSArray> receiver,
-                           Handle<FixedArrayBase> backing_store,
                            Arguments* args, uint32_t unshift_size) = 0;
 
   virtual Handle<JSArray> Slice(Handle<JSObject> receiver,
-                                Handle<FixedArrayBase> backing_store,
                                 uint32_t start, uint32_t end) = 0;
 
   virtual Handle<JSArray> Splice(Handle<JSArray> receiver,
-                                 Handle<FixedArrayBase> backing_store,
                                  uint32_t start, uint32_t delete_count,
                                  Arguments* args, uint32_t add_count) = 0;
 
-  virtual Handle<Object> Pop(Handle<JSArray> receiver,
-                             Handle<FixedArrayBase> backing_store) = 0;
+  virtual Handle<Object> Pop(Handle<JSArray> receiver) = 0;
 
-  virtual Handle<Object> Shift(Handle<JSArray> receiver,
-                               Handle<FixedArrayBase> backing_store) = 0;
+  virtual Handle<Object> Shift(Handle<JSArray> receiver) = 0;
 
  protected:
   friend class LookupIterator;