[ios] Recent Tabs: Hook up delegate for immediate UI update after signin

This needs to be hooked up so that the recent tabs
view controller immediately gets updated after coming
back from signin. Waiting for the synced session update
signal is not immediate enough.

Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I924156e8a76dfa4c702d7f8d0714a14588f74653
Reviewed-on: https://chromium-review.googlesource.com/1067246
Commit-Queue: edchin <edchin@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560388}

ios/chrome/browser/ui/recent_tabs/recent_tabs_coordinator.mm

@@ -66,6 +66,7 @@ - (void)start {
   // Set the consumer first before calling [self.mediator initObservers] and
   // then [self.mediator reloadSessions].
   self.mediator.consumer = recentTabsTableViewController;
+  recentTabsTableViewController.delegate = self.mediator;
   [self.mediator initObservers];
   [self.mediator reloadSessions];
 

ios/chrome/browser/ui/recent_tabs/recent_tabs_mediator.mm

@@ -152,6 +152,10 @@ - (void)reloadSessionsData {
 #pragma mark - RecentTabsTableViewControllerDelegate
 
 - (void)refreshSessionsView {
+  // This method is called from two places: 1) when this mediator observes a
+  // change in the synced session state, and 2) when the UI layer recognizes
+  // that the signin process has completed. The latter call is necessary because
+  // it can happen much more immediately than the former call.
   [self.consumer refreshUserState:[self userSignedInState]];
 }