Introduce a couple of abstract bases for WebDataService.

chrome/browser/api/webdata/web_data_service_consumer.h

Index: chrome/browser/api/webdata/web_data_service_consumer.h
diff --git a/chrome/browser/api/webdata/web_data_service_consumer.h b/chrome/browser/api/webdata/web_data_service_consumer.h
new file mode 100644
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+++ b/chrome/browser/api/webdata/web_data_service_consumer.h
@@ -0,0 +1,26 @@
+// Copyright (c) 2012 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 CHROME_BROWSER_API_WEBDATA_WEB_DATA_SERVICE_CONSUMER_H_
+#define CHROME_BROWSER_API_WEBDATA_WEB_DATA_SERVICE_CONSUMER_H_
+
+#include "chrome/browser/api/webdata/web_data_results.h"
+#include "chrome/browser/api/webdata/web_data_service_base.h"
+
+// All requests to the web data service are asynchronous. When the request has
+// been performed, the data consumer is notified using the following interface.
+class WebDataServiceConsumer {
+ public:
+  // Called when a request is done. h uniquely identifies the request.
+  // result can be NULL, if no result is expected or if the database could
+  // not be opened. The result object is destroyed after this call.
+  virtual void OnWebDataServiceRequestDone(WebDataServiceBase::Handle h,
+                                           const WDTypedResult* result) = 0;
+
+ protected:
+  virtual ~WebDataServiceConsumer() {}
+};
+
+
+#endif  // CHROME_BROWSER_API_WEBDATA_WEB_DATA_SERVICE_CONSUMER_H_