Remove all code related to the PreRead field trial.

chrome/browser/metrics/chrome_metrics_service_accessor.h

Index: chrome/browser/metrics/chrome_metrics_service_accessor.h
diff --git a/chrome/browser/metrics/chrome_metrics_service_accessor.h b/chrome/browser/metrics/chrome_metrics_service_accessor.h
index 333cd127c8693b4ed9870d43fd9aeceb073243fa..0b0b8818b338e3c7def5367348fe4a23a668000e 100644
--- a/chrome/browser/metrics/chrome_metrics_service_accessor.h
+++ b/chrome/browser/metrics/chrome_metrics_service_accessor.h
@@ -30,10 +30,6 @@ class ExternalDataUseObserverBridge;
 }
 }
 
-namespace chrome_browser {
-void SetupPreReadFieldTrial();
-}
-
 namespace component_updater {
 class ComponentUpdateService;
 }
@@ -87,7 +83,6 @@ class ChromeMetricsServiceAccessor : public metrics::MetricsServiceAccessor {
   friend class ArcSupportHost;
   friend class BrowserProcessImpl;
   friend void chrome::AttemptRestart();
-  friend void chrome_browser::SetupPreReadFieldTrial();
   friend class chrome::android::ExternalDataUseObserverBridge;
   friend class ChromeMetricsServicesManagerClient;
   friend class ChromeRenderMessageFilter;