buffer: Reallocate() instead of creating new backing store

Author: mildsunrise

src/node_buffer.cc

@@ -327,13 +327,8 @@ MaybeLocal<Object> New(Isolate* isolate,
     CHECK(actual <= length);
 
     if (LIKELY(actual > 0)) {
-      if (actual < length) {
-        std::unique_ptr<BackingStore> old_store = std::move(store);
-        store = ArrayBuffer::NewBackingStore(isolate, actual);
-        memcpy(static_cast<char*>(store->Data()),
-               static_cast<char*>(old_store->Data()),
-               actual);
-      }
+      if (actual < length)
+        store = BackingStore::Reallocate(isolate, std::move(store), actual);
       Local<ArrayBuffer> buf = ArrayBuffer::New(isolate, std::move(store));
       Local<Object> obj;
       if (UNLIKELY(!New(isolate, buf, 0, actual).ToLocal(&obj)))