Add an IPC method for Blink to call RapporService::RecordSample()

ios/web/public/user_metrics.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 IOS_WEB_PUBLIC_USER_METRICS_H_
 #define IOS_WEB_PUBLIC_USER_METRICS_H_
 
 #include <string>
 
 #include "base/callback.h"
 
 namespace base {
 struct UserMetricsAction;
 }  // namespace base
 
 namespace web {
 
 // Wrappers around functions defined in base/metrics/user_metrics.h, refer to
 // that header for full documentation. These wrappers can be called from any
 // thread (they will post back to the UI thread to do the recording).
 
 void RecordAction(const base::UserMetricsAction& action);
 void RecordComputedAction(const std::string& action);
+void RecordRappor(const std::string& metric, const std::string& sample);
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_USER_METRICS_H_