For reference, here is the error in Firefox

https://screenshot.googleplex.com/O8Fab0WaTzz

Another proposition is to have the same UI and disable the buttons.

https://screenshot.googleplex.com/xBsPqBDT9Ut

I prefer the alert view as it is easier to parse (or inversely to dismiss) and is the correct and expected type of UI for displaying a message to the user.

As for the strings:

Title: Chrome cannot handle this link.
Message: <invalid URL>

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1186149ec71795fd017d8fef851d2dd10c2a7b56

commit 1186149ec71795fd017d8fef851d2dd10c2a7b56
Author: olivierrobin <olivierrobin@chromium.org>
Date: Mon Jan 02 13:04:31 2017

Handle invalid URLs in share extension.

Show an error dialog is scheme is not HTTP or HTTPS.
Do not process item if scheme is not HTTP or HTTPS.

Adds olivierrobin@chromium.org as owner of
ios/chrome/browser/share_extension/

BUG= 677259 

Review-Url: https://codereview.chromium.org/2608913002
Cr-Commit-Position: refs/heads/master@{#441062}

[modify] https://crrev.com/1186149ec71795fd017d8fef851d2dd10c2a7b56/components/reading_list/ios/reading_list_model_impl.cc
[add] https://crrev.com/1186149ec71795fd017d8fef851d2dd10c2a7b56/ios/chrome/browser/share_extension/OWNERS
[modify] https://crrev.com/1186149ec71795fd017d8fef851d2dd10c2a7b56/ios/chrome/browser/share_extension/share_extension_item_receiver.mm
[modify] https://crrev.com/1186149ec71795fd017d8fef851d2dd10c2a7b56/ios/chrome/share_extension/share_extension_localize_strings_config.plist
[modify] https://crrev.com/1186149ec71795fd017d8fef851d2dd10c2a7b56/ios/chrome/share_extension/share_extension_view.mm
[modify] https://crrev.com/1186149ec71795fd017d8fef851d2dd10c2a7b56/ios/chrome/share_extension/share_view_controller.mm
[modify] https://crrev.com/1186149ec71795fd017d8fef851d2dd10c2a7b56/ios/chrome/share_extension/strings/ios_share_extension_strings.grd

olivier@, Do you have any websites or web pages examples I could use for testing this fix?

mmm
This is a good question indeed as you need a permissive application and a page presening bad URL.

You can test it by
1. installing firefox-ios
2. in firefox, visit http://browsingtest.appspot.com/external_url_links.html
3. long press on "Calendar URL"
4. Share link
5. Chrome

Note: in Chrome, the context menu for this link should be only "Copy".

Verified in 57.0.2978.0 canary, iPhone 6 plus 10.2, iPad mini 10.1

Error dialog is shown for for urls that are not HTTP or HTTPS.