The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/97a5a4ae3383aa0efa0fef804f7ced11a01db340

commit 97a5a4ae3383aa0efa0fef804f7ced11a01db340
Author: gambard <gambard@chromium.org>
Date: Mon Aug 07 17:39:21 2017

Add spinner when fetching more suggestions

When more suggestions are fetched on the NTP, a spinner is displayed
to signal the user the suggestions are being fetched.
This spinner prevents the user from interacting with the button.
If the suggestions couldn't be fetched (network error...) a toast is
displayed.
If there is no more suggestions, the footer is removed.

Bug:  721229 
Change-Id: Ib58fb446e76bbb752f37105135a58068713c96b5
Reviewed-on: https://chromium-review.googlesource.com/602130
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Elodie Banel <lod@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492350}
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/components/ntp_snippets_strings.grdp
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/content_suggestions/content_suggestions_mediator.mm
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/content_suggestions/mediator_util.h
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/content_suggestions/mediator_util.mm
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/ui/content_suggestions/cells/BUILD.gn
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/ui/content_suggestions/cells/content_suggestions_footer_item.h
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/ui/content_suggestions/cells/content_suggestions_footer_item.mm
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/ui/content_suggestions/cells/content_suggestions_footer_item_unittest.mm
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_updater.mm
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/ui/content_suggestions/content_suggestions_data_source.h
[modify] https://crrev.com/97a5a4ae3383aa0efa0fef804f7ced11a01db340/ios/chrome/browser/ui/settings/material_cell_catalog_view_controller.mm

Verified in Build - 62.0.3186.0 Canary -  iPhone 6 iOS 11 beta 6, iPad Mini 11 beta 6, 
The issue “Spinner when fetching additional suggestions” has been Verified now for the fix.