Remove all code related to the PreRead field trial.

chrome/browser/metrics/chrome_metrics_service_accessor.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 CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_ACCESSOR_H_
 #define CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_ACCESSOR_H_
 
 #include <stdint.h>
 #include <string>
 #include <vector>
@@ skipping 12 matching lines @@
 class FlashDOMHandler;
 }
 
 namespace chrome {
 void AttemptRestart();
 namespace android {
 class ExternalDataUseObserverBridge;
 }
 }
 
-namespace chrome_browser {
-void SetupPreReadFieldTrial();
-}
-
 namespace component_updater {
 class ComponentUpdateService;
 }
 
 namespace domain_reliability {
 class DomainReliabilityServiceFactory;
 }
 
 namespace extensions {
 class ChromeExtensionWebContentsObserver;
@@ skipping 33 matching lines @@
 // This class limits and documents access to metrics service helper methods.
 // Since these methods are private, each user has to be explicitly declared
 // as a 'friend' below.
 class ChromeMetricsServiceAccessor : public metrics::MetricsServiceAccessor {
  private:
   friend class ::CrashesDOMHandler;
   friend class ::FlashDOMHandler;
   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;
   friend class DataReductionProxyChromeSettings;
   friend class domain_reliability::DomainReliabilityServiceFactory;
   friend class extensions::ChromeExtensionWebContentsObserver;
   friend class extensions::FileManagerPrivateIsUMAEnabledFunction;
   friend class extensions::MetricsPrivateGetIsCrashReportingEnabledFunction;
   friend void ChangeMetricsReportingStateWithReply(
       bool,
@@ skipping 40 matching lines @@
   // with g_browser_process->metrics_service(). See that function's declaration
   // for details.
   static bool RegisterSyntheticFieldTrialWithNameHash(
       uint32_t trial_name_hash,
       const std::string& group_name);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(ChromeMetricsServiceAccessor);
 };
 
 #endif  // CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_ACCESSOR_H_