The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9899ff1dc301161eacfdaefe29f4b0a30da06181

commit 9899ff1dc301161eacfdaefe29f4b0a30da06181
Author: Mathieu Perreault <mathp@chromium.org>
Date: Mon May 07 16:23:39 2018

[Payment Request] Add the Payment Handler icon to the window.

Payment Handler instrument icon was only shown in the Payment Sheet. Now it is
shown as a 32x32 "favicon" in the Payment Handler window.

Bug:  840056 
Change-Id: Id4df874e0443fd5479b301a6dacd8bdece52382e
Reviewed-on: https://chromium-review.googlesource.com/1045865
Reviewed-by: anthonyvd <anthonyvd@chromium.org>
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Commit-Queue: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556465}
[modify] https://crrev.com/9899ff1dc301161eacfdaefe29f4b0a30da06181/chrome/browser/ui/views/payments/payment_handler_web_flow_view_controller.cc
[modify] https://crrev.com/9899ff1dc301161eacfdaefe29f4b0a30da06181/chrome/browser/ui/views/payments/payment_request_views_util.cc

Tried testing the issue on mac 10.13.3, win-10 and ubuntu 14.04 using chrome version #68.0.3424.0 from comment #0.
Observed that after navigating to url: https://www.google.com/url?q=https://rsolomakhin.github.io/&sa=D&source=hangouts&ust=1525867971344000&usg=AFQjCNHmRsOLjb6CGt94JRVflWCYh4NNfQ and clicking on the link "bob pay" and after clicking the "buy" button received an error as follows:
Cannot make payment
NotSupportedError: The payment methods "https://emerald-eon.appspot.com/bobpay", "interledger" are not supported.

Attaching screen shot for reference.

mathp@ - Could you please check the attached screen shot and please let us know if any flag need to be enabled or any pre-condition need to be performed in order to verify the issue.

Thanks...!!

Deleted: 840056.png 464 KB

	840056.png 464 KB View Download

1) chrome://flags/#service-worker-payment-apps
2) Visit https://bobpay.xyz and click on "Install BobPay Web Payment App"
3) Visit https://rsolomakhin.github.io/pr/bob, click "Buy", then "Pay". 
4) should see the tree icon as shown above.