Mark, do these heuristics seem like a good first pass?  Additionally, would this text be scaled based on the system font setting?  Not sure what the guidelines are on which labels should be scaled; I believe it's mostly for long-form readable content, but we can do it here as well if desired.

These sound like reasonable heuristics.

As far as scaling goes, feel free to read the Dynamic Type guidelines and make a recommendation.

Pri-0 bugs are critical regressions or serious emergencies, and this bug has not been updated in three days. Could you please provide an update, or adjust the priority to a more appropriate level if applicable?

If a fix is in active development, please set the status to Started.

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crrev.com/c/1018168

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/895e2c4c02a01e7e218a6302d2756729262d8115

commit 895e2c4c02a01e7e218a6302d2756729262d8115
Author: Kurt Horimoto <kkhorimoto@chromium.org>
Date: Fri Apr 20 01:57:05 2018

[iOS] Truncate OverscrollActionView labels to be half the view's width.

This can be useful for localized translations of these labels, which
may need to span multiple lines.

Bug:  805100 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I4a4a8b98cb8b7f56f5b7b19dbe8478bf50f4fbf2
Reviewed-on: https://chromium-review.googlesource.com/1018168
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552229}
[modify] https://crrev.com/895e2c4c02a01e7e218a6302d2756729262d8115/ios/chrome/browser/ui/overscroll_actions/overscroll_actions_view.mm

The NextAction date has arrived: 2018-04-25