Add BytesRead metric to CPM

chrome/browser/performance_monitor/metric_details.h

 // 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_PERFORMANCE_MONITOR_METRIC_DETAILS_H_
 #define CHROME_BROWSER_PERFORMANCE_MONITOR_METRIC_DETAILS_H_
 
 #include <string>
 
 namespace performance_monitor {
 
 // Keep this enum synced with kMetricDetailsList in the cc file.
 enum MetricType {
   METRIC_CPU_USAGE,
   METRIC_PRIVATE_MEMORY_USAGE,
   METRIC_SHARED_MEMORY_USAGE,
   METRIC_STARTUP_TIME,
   METRIC_TEST_STARTUP_TIME,
   METRIC_SESSION_RESTORE_TIME,
   METRIC_PAGE_LOAD_TIME,
+  METRIC_BYTES_READ,
   METRIC_NUMBER_OF_METRICS
 };
 
 struct MetricDetails {
   const char* const name;
   const char* const description;
   const char* const units;
   const double tick_size;
 };
 
 const MetricDetails* GetMetricDetails(MetricType event_type);
 
 }  // namespace performance_monitor
 
 #endif  // CHROME_BROWSER_PERFORMANCE_MONITOR_METRIC_DETAILS_H_