Replace hand-written IDBObserverCallback with auto-generated code

third_party/WebKit/Source/modules/indexeddb/IDBObserverCallback.h

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef IDBObserverCallback_h
-#define IDBObserverCallback_h
-
-#include "platform/heap/Handle.h"
-
-namespace blink {
-
-class ExecutionContext;
-class IDBObserver;
-class IDBObserverChanges;
-
-class IDBObserverCallback
-    : public GarbageCollectedFinalized<IDBObserverCallback> {
- public:
-  virtual ~IDBObserverCallback() {}
-  virtual void handleChanges(IDBObserverChanges&, IDBObserver&) = 0;
-  virtual ExecutionContext* getExecutionContext() const = 0;
-  DEFINE_INLINE_VIRTUAL_TRACE() {}
-};
-
-}  // namespace blink
-
-#endif  // IDBObserverCallback_h