OK, I've done some investigation and realised a couple of things:

- my test site is kind of broken. The 'Read Location Delayed' button never works in this situation (on Android, with system location turned off). This is by design - there is no gesture associated with the permission request, which happens on a timer.

- as a result I don't think it would be possible for a normal site to prompt for location from the background. I'll do some more investigation about whether the DSE (which doesn't require a gesture) can make this come up.

OK ... turns out this could be a problem for the DSE. Uploading a fix now, should have it out for review soon.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b8a8a089caa1188776c83e4344df494d6f30b969

commit b8a8a089caa1188776c83e4344df494d6f30b969
Author: benwells <benwells@chromium.org>
Date: Wed Apr 19 22:53:03 2017

Don't show the Location Settings Dialog if the tab isn't interactable.

If the tab for the web_contents that requested location isn't interactable, the Location Settings Dialog shouldn't be shown. This could happen if the user changed tabs, is in the tab switcher, or if Chrome isn't active.

BUG= 710255 

Review-Url: https://codereview.chromium.org/2817873002
Cr-Commit-Position: refs/heads/master@{#465795}

[modify] https://crrev.com/b8a8a089caa1188776c83e4344df494d6f30b969/chrome/browser/geolocation/geolocation_permission_context_android.cc

Tested on canary

Your change meets the bar and is auto-approved for M59. Please go ahead and merge the CL to branch 3071 manually. Please contact milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), gkihumba@(ChromeOS), Abdul Syed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/196648220d843aa53efaf3f123ba49476f3f2f8c

commit 196648220d843aa53efaf3f123ba49476f3f2f8c
Author: Ben Wells <benwells@chromium.org>
Date: Mon Apr 24 07:12:41 2017

Don't show the Location Settings Dialog if the tab isn't interactable.

If the tab for the web_contents that requested location isn't interactable, the Location Settings Dialog shouldn't be shown. This could happen if the user changed tabs, is in the tab switcher, or if Chrome isn't active.

BUG= 710255 

Review-Url: https://codereview.chromium.org/2817873002
Cr-Commit-Position: refs/heads/master@{#465795}
(cherry picked from commit b8a8a089caa1188776c83e4344df494d6f30b969)

Review-Url: https://codereview.chromium.org/2835923002 .
Cr-Commit-Position: refs/branch-heads/3071@{#156}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}

[modify] https://crrev.com/196648220d843aa53efaf3f123ba49476f3f2f8c/chrome/browser/geolocation/geolocation_permission_context_android.cc