[ios] Fixes an infinite sync loop in RecentTabsMediator.

|reloadSessions| previously had code to trigger another sync refresh.
The old sync sessions implementation would detect that nothing had
changed and break the update cycle, but a new implementation notifies
observers unconditionally.  This was leading to an infinite loop of sync
updates.

BUG=854049

Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I85dbf2810f5ff6e009812a33ad643fb54cfdc8c4
Reviewed-on: https://chromium-review.googlesource.com/1106001Reviewed-by: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568476}

ios/chrome/browser/ui/ntp/recent_tabs/legacy_recent_tabs_table_coordinator.mm

@@ -53,7 +53,7 @@
 - (void)start {
   _tableViewController.handsetCommandHandler = self.handsetCommandHandler;
   [self.mediator initObservers];
-  [self.mediator reloadSessions];
+  [self.mediator configureConsumer];
 }
 
 - (void)stop {

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

@@ -65,7 +65,7 @@
   self.mediator = [[RecentTabsMediator alloc] init];
   self.mediator.browserState = self.browserState;
   // Set the consumer first before calling [self.mediator initObservers] and
-  // then [self.mediator reloadSessions].
+  // then [self.mediator configureConsumer].
   self.mediator.consumer = recentTabsTableViewController;
   // TODO(crbug.com/845636) : Currently, the image data source must be set
   // before the mediator starts updating its consumer. Fix this so that order of
@@ -73,7 +73,7 @@
   recentTabsTableViewController.imageDataSource = self.mediator;
   recentTabsTableViewController.delegate = self.mediator;
   [self.mediator initObservers];
-  [self.mediator reloadSessions];
+  [self.mediator configureConsumer];
 
   // Present RecentTabsNavigationController.
   self.recentTabsNavigationController = [[TableViewNavigationController alloc]

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

@@ -26,9 +26,15 @@ class ChromeBrowserState;
 // accordingly.
 @interface RecentTabsMediator
     : NSObject<ClosedTabsObserving,
-               RecentTabsImageDataSource,
-               SyncedSessionsObserver,
-               LegacyRecentTabsTableViewControllerDelegate>
+               LegacyRecentTabsTableViewControllerDelegate,
+               RecentTabsImageDataSource>
+
+// The consumer for this object. This can change during the lifetime of this
+// object and may be nil.
+@property(nonatomic, strong) id<RecentTabsTableConsumer> consumer;
+
+// The coordinator's BrowserState.
+@property(nonatomic, assign) ios::ChromeBrowserState* browserState;
 
 // Starts observing the he user's signed-in and chrome-sync states.
 - (void)initObservers;
@@ -36,12 +42,10 @@ class ChromeBrowserState;
 // Disconnects the mediator from all observers.
 - (void)disconnect;
 
-// The consumer for this object. This can change during the lifetime of this
-// object and may be nil.
-@property(nonatomic, strong) id<RecentTabsTableConsumer> consumer;
+// Configures the consumer with current data. Intended to be called immediately
+// after initialization.
+- (void)configureConsumer;
 
-// The coordinator's BrowserState.
-@property(nonatomic, assign) ios::ChromeBrowserState* browserState;
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_RECENT_TABS_RECENT_TABS_MEDIATOR_H_

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

@@ -30,7 +30,7 @@ const CGFloat kFaviconWidthHeight = 24;
 const CGFloat kFaviconMinWidthHeight = 16;
 }  // namespace
 
-@interface RecentTabsMediator () {
+@interface RecentTabsMediator ()<SyncedSessionsObserver> {
   std::unique_ptr<synced_sessions::SyncedSessionsObserverBridge>
       _syncedSessionsObserver;
   std::unique_ptr<recent_tabs::ClosedTabsObserverBridge> _closedTabsObserver;
@@ -47,8 +47,6 @@ const CGFloat kFaviconMinWidthHeight = 16;
 - (BOOL)isSyncCompleted;
 // Reload the panel.
 - (void)refreshSessionsView;
-// Force a contact to the sync server to reload remote sessions.
-- (void)reloadSessionsData;
 
 @end
 
@@ -88,10 +86,13 @@ const CGFloat kFaviconMinWidthHeight = 16;
   }
 }
 
+- (void)configureConsumer {
+  [self refreshSessionsView];
+}
+
 #pragma mark - SyncedSessionsObserver
 
 - (void)reloadSessions {
-  [self reloadSessionsData];
   [self refreshSessionsView];
 }
 
@@ -168,13 +169,6 @@ const CGFloat kFaviconMinWidthHeight = 16;
   return _syncedSessionsObserver->IsFirstSyncCycleCompleted();
 }
 
-- (void)reloadSessionsData {
-  const syncer::ModelTypeSet types(syncer::SESSIONS);
-  // Requests a sync refresh of the sessions for the current profile.
-  ProfileSyncServiceFactory::GetForBrowserState(_browserState)
-      ->TriggerRefresh(types);
-}
-
 #pragma mark - RecentTabsTableViewControllerDelegate
 
 - (void)refreshSessionsView {