Add peak memory usage metric

chrome/browser/metrics/chrome_metrics_service_client.h

Index: chrome/browser/metrics/chrome_metrics_service_client.h
diff --git a/chrome/browser/metrics/chrome_metrics_service_client.h b/chrome/browser/metrics/chrome_metrics_service_client.h
index 16f59c6e688d2d37b94733f85998a1af9377f82f..10c06f538ee93f185b9d812b83ecf2647c6edb27 100644
--- a/chrome/browser/metrics/chrome_metrics_service_client.h
+++ b/chrome/browser/metrics/chrome_metrics_service_client.h
@@ -203,6 +203,10 @@ class ChromeMetricsServiceClient
   // MemoryDetails.
   MemoryGrowthTracker memory_growth_tracker_;
 
+  // The PeakMemoryUsageTracker instance that tracks peak memory usage in
+  // MemoryDetails.
+  PeakMemoryUsageTracker peak_memory_usage_tracker_;
+
   // Callback to determine whether or not a cellular network is currently being
   // used.
   base::Callback<void(bool*)> cellular_callback_;