rAc: make requestAutocomplete() return a promise.

Source/core/dom/AutocompleteError.h

+// Copyright 2014 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 AutocompleteError_h
+#define AutocompleteError_h
+
+#include "core/dom/DOMException.h"
+#include "heap/Handle.h"
+#include "wtf/PassRefPtr.h"
+#include "wtf/RefCounted.h"
+
+namespace WebCore {
+
+class AutocompleteError : public DOMException {
+public:
+    static PassRefPtrWillBeRawPtr<AutocompleteError> create(const String& reason)
+    {
+        return adoptRefWillBeNoop(new AutocompleteError(reason));
+    }
+
+    const String& reason() const { return m_reason; }
+
+private:
+    explicit AutocompleteError(const String& reason);
+    const String m_reason;
+};
+
+} // namespace WebCore
+
+#endif // AutocompleteError_h