Which one looks better and is more harmonious with the current design? 
I'm assuming the UIActivityIndicator. If that is correct, please use it. 
Having said that, please let us know if the overhead of replacing the MDC one is too large to justify the effort. This falls in the nice-to-have bucket. 

I've been leaning towards using UIActivityIndicator because I think it has some benefits in scenarios where it is shown/hid quickly (you get a sense of a progress indicator vs the MDC variant that requires more time to make itself visible and understood). I also prefer it visually.

That being said, I just noticed that in addition to the header indicator discussed in this bug, we also show an indictor centered in the screen's bounds just after tapping "Enable Sync" (in a scenario where there are no associated accounts). Further, when the sign in VC is invoked, there is also an MDC indicator there.

Because I would want to remain consistent in our indicator usage app-wide (I'm not sure if there are other instances other than ones mentioned here), and because it is used in VCs that I assume we can't easily augment (sign in), I'm leaning towards leaving this as is for phase 1.

Sergio/Chris: can you give me a quick idea of the MDC indicator's API? The main thing I'm interested in is the ability to set a color and the size.

We can set the radius (Defaults to 12dp (24x24dp circle), constrained to range [8dp, 72dp].) and strokeWidth.

There's also an array of colors we can set (The array of colors that are cycled through when animating the spinner.) I guess if we create an array with just one color its going to stay that way.

So I just landed a CL that implements UIActivityIndicator. I personally prefer this over MDC also, but if you want to keep things consistent, I can swap it out with MDC. It's not difficult at all.

Here is the CL: https://chromium-review.googlesource.com/c/chromium/src/+/1011351

Also, there's an MDC loading indicator on History and Bookmarks while they're fetching data. Though they both do it differently:
History adds a cell with an MDC loading indicator to the table, so this indicator is right under the navigation bar (closer to the top of the screen).
Bookmarks adds a view with a loading indicator on top of the table (on the middle of the screen pretty much.)

I prefer Bookmarks approach and I think we should definitely standardize this.

Martijn/Pete WDYT? 

FWIW, I prefer the bookmarks treatment over History's. 
I defer to Pete/Martijn/Sergio for the final call on which indicator to use and how but yes, let's be consistent please.

I am not able to repo the two treatments mentioned in #6, but I can picture it and I think it is a general good practice to do as Bookmarks does and center [vertically and horizontally] the indicator in the view that is devoid of and loading content. This is not a hard and fast rule, but in general it is a pretty safe and sane pattern to follow.

In regards to which indicator to use, Martijn and I think we should **stick with MDC for phase 1** as it will be easier to ensure we are consistent app-wide.

We can reassess the situation after m69 and if we decide a change is warranted, we can do so in a sweeping app-wide pass (for example, if we are going to be materially/chromey/googley, I would love to create something as polished as this eventually: http://material-design.storage.googleapis.com/videos/components-progressandactivity-progressandactivity-_20spec.circular_201_large_xhdpi.webm)

Chris: in terms of specs for this view, I'd say be consistent with the other [similar] instances of the MDC indicator view in-app (sounds like it might be 12pt radius, an array of a single blue color, as I don't recall seeing the "rainbow" effect in our app, and I'm not sure what for the strokeWidth ... again, do what we do elsewhere).

Ok thanks Pete! I'll open another CL that changed it back to MDC.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4faeffef9bf31d1f0595c1efc5c07ea8f3051aa7

commit 4faeffef9bf31d1f0595c1efc5c07ea8f3051aa7
Author: Chris Lu <thegreenfrog@chromium.org>
Date: Mon Apr 23 23:35:44 2018

[ios] use MDC instead of UIactivityindicator in Recent Tabs

Keeping things consistent in Bijou Phase 1

https://drive.google.com/file/d/14nkloZ4PX0UD0HnXZgMLKYo6-iUzn5kt/view?usp=sharing


Bug:  833623 
Change-Id: Ie5aeaac7c3787775d4845aa6cb030236b6de9c2f
Reviewed-on: https://chromium-review.googlesource.com/1022173
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552899}
[modify] https://crrev.com/4faeffef9bf31d1f0595c1efc5c07ea8f3051aa7/ios/chrome/browser/ui/table_view/cells/BUILD.gn
[modify] https://crrev.com/4faeffef9bf31d1f0595c1efc5c07ea8f3051aa7/ios/chrome/browser/ui/table_view/cells/table_view_activity_indicator_header_footer_item.mm

The NextAction date has arrived: 2018-05-09

What should the next action be in this case? I see that it was set to May 9th on the day the issue was marked as fixed.