[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 f25c671a3a249884747f31e4ecb2b061defc5fe1..5559c5ba05508b4fe91411dab26d3f802b980410 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
@@ -1654,6 +1654,12 @@ 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];
+    }
   }
 }