Upstream helper method to clear data using BrowserStateDataRemover.

ios/chrome/browser/signin/browser_state_data_remover.mm

 // 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.
 
 #import "ios/chrome/browser/signin/browser_state_data_remover.h"
 
 #include "base/logging.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/prefs/pref_service.h"
 #include "components/signin/core/common/signin_pref_names.h"
@@ skipping 11 matching lines @@
     : browser_state_(browser_state), forget_last_username_(false) {
   callback_subscription_ =
       IOSChromeBrowsingDataRemover::RegisterOnBrowsingDataRemovedCallback(
           base::Bind(&BrowserStateDataRemover::NotifyWithDetails,
                      base::Unretained(this)));
 }
 
 BrowserStateDataRemover::~BrowserStateDataRemover() {
 }
 
+// static
+void BrowserStateDataRemover::ClearData(ios::ChromeBrowserState* browser_state,
+                                        ProceduralBlock completion) {
+  // The user just changed the account and chose to clear the previously
+  // existing data. As browsing data is being cleared, it is fine to clear the
+  // last username, as there will be no data to be merged.
+  BrowserStateDataRemover* remover = new BrowserStateDataRemover(browser_state);
+  remover->SetForgetLastUsername();
+  remover->RemoveBrowserStateData(completion);
+}
+
 void BrowserStateDataRemover::SetForgetLastUsername() {
   forget_last_username_ = true;
 }
 
 void BrowserStateDataRemover::RemoveBrowserStateData(ProceduralBlock callback) {
   DCHECK(!callback_);
   callback_.reset([callback copy]);
 
   base::scoped_nsobject<ClearBrowsingDataCommand> command(
       [[ClearBrowsingDataCommand alloc]
@@ skipping 23 matching lines @@
   if (forget_last_username_) {
     browser_state_->GetPrefs()->ClearPref(prefs::kGoogleServicesLastAccountId);
     browser_state_->GetPrefs()->ClearPref(prefs::kGoogleServicesLastUsername);
   }
 
   if (callback_)
     callback_.get()();
 
   base::ThreadTaskRunnerHandle::Get()->DeleteSoon(FROM_HERE, this);
 }