Define a new policy to disable clearing the browsing history from the UI.

chrome/browser/ui/webui/settings/settings_clear_browsing_data_handler.h

Index: chrome/browser/ui/webui/settings/settings_clear_browsing_data_handler.h
diff --git a/chrome/browser/ui/webui/settings/settings_clear_browsing_data_handler.h b/chrome/browser/ui/webui/settings/settings_clear_browsing_data_handler.h
index 7672c068195e4c32542f49833cab1813a047a1e6..57b97f77a3ff4a7b2ed490d38b0656c2a3216a68 100644
--- a/chrome/browser/ui/webui/settings/settings_clear_browsing_data_handler.h
+++ b/chrome/browser/ui/webui/settings/settings_clear_browsing_data_handler.h
@@ -16,7 +16,6 @@
 #include "chrome/browser/ui/webui/settings/settings_page_ui_handler.h"
 #include "components/browser_sync/profile_sync_service.h"
 #include "components/browsing_data/core/counters/browsing_data_counter.h"
-#include "components/prefs/pref_change_registrar.h"
 
 namespace base {
 class ListValue;
@@ -52,9 +51,6 @@ class ClearBrowsingDataHandler : public SettingsPageUIHandler,
   // by the WebUI action that initiated it.
   void OnClearingTaskFinished(const std::string& webui_callback_id);
 
-  // Updates UI when the pref to allow clearing history changes.
-  virtual void OnBrowsingHistoryPrefChanged();
-
   // Initializes the dialog UI. Called by JavaScript when the DOM is ready.
   void HandleInitialize(const base::ListValue* args);
 
@@ -96,9 +92,6 @@ class ClearBrowsingDataHandler : public SettingsPageUIHandler,
   ScopedObserver<browser_sync::ProfileSyncService, syncer::SyncServiceObserver>
       sync_service_observer_;
 
-  // Used to listen for pref changes to allow / disallow deleting browsing data.
-  PrefChangeRegistrar profile_pref_registrar_;
-
   // Whether the sentence about other forms of history stored in user's account
   // should be displayed in the footer. This value is retrieved asynchronously,
   // so we cache it here.