[ios] Set favicon fallback style for UI Refresh for ReadingList

- Sets the fallback monogram and background colors to a constant color.

Collections flag off screenshot: https://drive.google.com/file/d/10fYA9oHwx_o3cGWXBSR5P4qXKIPDTcfm/view?usp=sharing
Collections flag on screenshot: https://drive.google.com/file/d/1WtAYb-fPE6QdR4rIpcWxuZtLjGr7iPNQ/view?usp=sharing

Bug: 851390

Change-Id: I7d67a4129263b2deed52eb7603b3f84aa8b8a201
Reviewed-on: https://chromium-review.googlesource.com/1125271
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574582}
1 file changed