Change return type of Tab -navigationManager.

ios/chrome/browser/tabs/tab.h

Index: ios/chrome/browser/tabs/tab.h
diff --git a/ios/chrome/browser/tabs/tab.h b/ios/chrome/browser/tabs/tab.h
index eb88fc6f64f4b2b9f5333a226bac2301d3044c3c..5115735515c7be0d7399bdbe028f05f93380e6ab 100644
--- a/ios/chrome/browser/tabs/tab.h
+++ b/ios/chrome/browser/tabs/tab.h
@@ -57,6 +57,7 @@ struct SessionTab;
 
 namespace web {
 class NavigationItem;
+class NavigationManager;
 class NavigationManagerImpl;
 struct Referrer;
 class WebState;
@@ -244,7 +245,10 @@ extern NSString* const kProxyPassthroughHeaderValue;
 
 // Returns the NavigationManager for this tab's WebState. Requires WebState to
 // be populated. Can return null.
-- (web::NavigationManagerImpl*)navigationManager;
+// TODO(crbug.com/620465): remove navigationManagerImpl once Tab no longer uses
+// nor exposes private ios/web/ API.
+- (web::NavigationManager*)navigationManager;
+- (web::NavigationManagerImpl*)navigationManagerImpl;
 
 // Update the tab's history by replacing all previous navigations with
 // |navigations|.