[ios] Sets the content suggestions offset after a delay

Since the Discover feed uses a diffable data source its not completely
loaded at this time, in order to make this work we need to add a short
delay before scrolling.

Bug: 1108403
Change-Id: Id40dcc0655fe3fe01fdd4966611c475dce44bcca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587474Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836636}

ios/chrome/browser/ui/content_suggestions/content_suggestions_view_controller.mm

@@ -60,6 +60,8 @@ const CGFloat kDiscoverFeedFeaderHeight = 30;
 // Minimum height of the Discover feed content to indicate that the articles
 // have loaded.
 const CGFloat kDiscoverFeedLoadedHeight = 1000;
+// Delay before the CollectionView scrolls to the saved position.
+const CGFloat kDelayBeforeScrollingToSavedOffset = 0.3;
 }
 
 NSString* const kContentSuggestionsMostVisitedAccessibilityIdentifierPrefix =
@@ -952,9 +954,25 @@ NSString* const kContentSuggestionsMostVisitedAccessibilityIdentifierPrefix =
                        self.traitCollection.preferredContentSizeCategory) +
                    collection.contentInset.bottom));
     if (collection.contentOffset.y != offset) {
-      collection.contentOffset = CGPointMake(0, offset);
-      // Update the constraints in case the omnibox needs to be moved.
-      [self updateConstraints];
+      // Since the Discover feed uses a diffable data source its not completely
+      // loaded at this time, in order to make this work we need to add a short
+      // delay before scrolling.
+      if (IsDiscoverFeedEnabled()) {
+        dispatch_after(dispatch_time(DISPATCH_TIME_NOW,
+                                     static_cast<int64_t>(
+                                         kDelayBeforeScrollingToSavedOffset *
+                                         NSEC_PER_SEC)),
+                       dispatch_get_main_queue(), ^{
+                         collection.contentOffset = CGPointMake(0, offset);
+                         // Update the constraints in case the omnibox needs to
+                         // be moved.
+                         [self updateConstraints];
+                       });
+      } else {
+        collection.contentOffset = CGPointMake(0, offset);
+        // Update the constraints in case the omnibox needs to be moved.
+        [self updateConstraints];
+      }
     }
   }
   _initialContentOffset = NAN;