Upstream helper method to clear data using BrowserStateDataRemover.

BUG=None

Review-Url: https://codereview.chromium.org/2390003003
Cr-Commit-Position: refs/heads/master@{#422785}

ios/chrome/browser/signin/browser_state_data_remover.h

@@ -20,6 +20,12 @@ class BrowserStateDataRemover {
   explicit BrowserStateDataRemover(ios::ChromeBrowserState* browser_state);
   ~BrowserStateDataRemover();
 
+  // Removes all bookmarks, clears all browsing data, last signed-in username
+  // and then runs |completion|. The user must be signed out when this method
+  // is called.
+  static void ClearData(ios::ChromeBrowserState* browser_state,
+                        ProceduralBlock completion);
+
   // If set then the last username will be removed from the browser state prefs
   // after the data has been wiped.
   void SetForgetLastUsername();

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;
 }