Upstream helper method to clear data using BrowserStateDataRemover.

ios/chrome/browser/signin/browser_state_data_remover.mm

Index: ios/chrome/browser/signin/browser_state_data_remover.mm
diff --git a/ios/chrome/browser/signin/browser_state_data_remover.mm b/ios/chrome/browser/signin/browser_state_data_remover.mm
index a8f55d81388638c7553a809f7ab62d9e8897506e..7a3ba5c81e575997b5204577a005b2f803830a10 100644
--- a/ios/chrome/browser/signin/browser_state_data_remover.mm
+++ b/ios/chrome/browser/signin/browser_state_data_remover.mm
@@ -29,6 +29,17 @@ BrowserStateDataRemover::BrowserStateDataRemover(
 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;
 }