[ios] Make sure that |didFinishNavigation| is signalled for fast goBack.

ios/web/web_state/ui/crw_wk_web_view_web_controller.mm

Index: ios/web/web_state/ui/crw_wk_web_view_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_wk_web_view_web_controller.mm b/ios/web/web_state/ui/crw_wk_web_view_web_controller.mm
index 2c2b1e320076d2a769b891cf9fb8d4b848cc3cbd..040f61392d254a71b52580c85759dd61466c7a59 100644
--- a/ios/web/web_state/ui/crw_wk_web_view_web_controller.mm
+++ b/ios/web/web_state/ui/crw_wk_web_view_web_controller.mm
@@ -1616,6 +1616,12 @@ WKWebViewErrorSource WKWebViewErrorSourceFromError(NSError* error) {
     [self addActivityIndicatorTask];
   } else {
     [self clearActivityIndicatorTasks];
+    if ([self currentBackForwardListItemHolder]->navigation_type() ==
+        WKNavigationTypeBackForward) {
+      // A fast back/forward may not call |webView:didFinishNavigation:|, so
+      // finishing the navigation should be signalled explicitly.
+      [self didFinishNavigation];
+    }
   }
 }