Domain Reliability: Add sample_rate field to Beacon

components/domain_reliability/beacon.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 COMPONENTS_DOMAIN_RELIABILITY_BEACON_H_
 #define COMPONENTS_DOMAIN_RELIABILITY_BEACON_H_
 
 #include <string>
 
 #include "base/memory/scoped_vector.h"
@@ skipping 50 matching lines @@
   int http_response_code;
   // Elapsed time between starting and completing the request.
   base::TimeDelta elapsed;
   // Start time of the request.  Encoded as the request age in the final JSON.
   base::TimeTicks start_time;
   // Length of the chain of Domain Reliability uploads leading to this report.
   // Zero if the request was not caused by an upload, one if the request was
   // caused by an upload that itself contained no beacons caused by uploads,
   // et cetera.
   int upload_depth;
+  // The probability that this request had of being reported ("sample rate").
+  double sample_rate;
 
   // Okay to copy and assign.
 };
 
 }  // namespace domain_reliability
 
 #endif  // COMPONENTS_DOMAIN_RELIABILITY_BEACON_H_