Reading List: Mark entry read when opening external app.

ios/chrome/browser/tabs/tab.mm

Index: ios/chrome/browser/tabs/tab.mm
diff --git a/ios/chrome/browser/tabs/tab.mm b/ios/chrome/browser/tabs/tab.mm
index b5e12d3765c2add415dff86d912e2a3beaf136a6..f98f5c6f75ff314d7a300912ef2f0045018b17c0 100644
--- a/ios/chrome/browser/tabs/tab.mm
+++ b/ios/chrome/browser/tabs/tab.mm
@@ -68,6 +68,8 @@
 #import "ios/chrome/browser/passwords/password_controller.h"
 #import "ios/chrome/browser/passwords/passwords_ui_delegate_impl.h"
 #include "ios/chrome/browser/pref_names.h"
+#include "ios/chrome/browser/reading_list/reading_list_model_factory.h"
+#import "ios/chrome/browser/reading_list/reading_list_web_state_observer.h"
 #include "ios/chrome/browser/search_engines/template_url_service_factory.h"
 #include "ios/chrome/browser/sessions/ios_chrome_session_tab_helper.h"
 #include "ios/chrome/browser/signin/account_consistency_service_factory.h"
@@ -1316,6 +1318,13 @@ void TabInfoBarObserver::OnInfoBarReplaced(infobars::InfoBar* old_infobar,
   return NO;
 }
 
+- (void)currentNavigationWillContinueInExternalApp {
+  ReadingListModel* model =
+      ReadingListModelFactory::GetForBrowserState(browserState_);
+  ReadingListWebStateObserver::FromWebState(webStateImpl_.get(), model)
+      ->CurrentNavigationWillContinueInExternalApp();
+}
+
 - (void)webState:(web::WebState*)webState
     didFinishNavigation:(web::NavigationContext*)navigation {
   if (navigation->IsSameDocument()) {