Adds EnableReadingList experimental flag.

ios/chrome/browser/experimental_flags.mm

 // Copyright 2015 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.
 
 // This file can be empty. Its purpose is to contain the relatively short lived
 // definitions required for experimental flags.
 
 #include "ios/chrome/browser/experimental_flags.h"
 
 #include <dispatch/dispatch.h>
@@ skipping 10 matching lines @@
 #include "ios/chrome/browser/chrome_switches.h"
 #include "ios/web/public/web_view_creation_util.h"
 
 namespace {
 NSString* const kEnableAlertOnBackgroundUpload =
     @"EnableAlertsOnBackgroundUpload";
 NSString* const kEnableViewCopyPasswords = @"EnableViewCopyPasswords";
 NSString* const kHeuristicsForPasswordGeneration =
     @"HeuristicsForPasswordGeneration";
 const char* const kWKWebViewTrialName = "IOSUseWKWebView";
+NSString* const kEnableReadingList = @"EnableReadingList";
 
 enum class WKWebViewEligibility {
   // UNSET indicates that no explicit call to set eligibility has been made,
   // nor has a default value been assumed due to checking eligibility.
   UNSET,
   ELIGIBLE,
   INELIGIBLE
 };
 WKWebViewEligibility g_wkwebview_trial_eligibility =
     WKWebViewEligibility::UNSET;
@@ skipping 190 matching lines @@
   } else if (command_line->HasSwitch(switches::kDisableTabSwitcher)) {
     return false;
   }
 
   // Check if the finch experiment is turned on.
   std::string group_name = base::FieldTrialList::FindFullName("IOSTabSwitcher");
   return base::StartsWith(group_name, "Enabled",
                           base::CompareCase::INSENSITIVE_ASCII);
 }
 
+bool IsReadingListEnabled() {
+  return [[NSUserDefaults standardUserDefaults] boolForKey:kEnableReadingList];
+}
+
 }  // namespace experimental_flags