Fixed steps:

Repro steps:
1) In chrome://flags disable "Improved Add to Homescreen"
2) Navigates to https://tests.peter.sh/notification-generator/
3) Tap "Add to Home screen" in the app menu
4) Launch the web app
5) "Tap" the "Display the notification" <button> on the web page. This should generate a notification
6) Tap on the "Peter Beverloo" link at the bottom of the page
7) Tap on the notification

Expected:
The webapp navigates to https://tests.peter.sh/notification-generator/
Actual:
The webapp does not navigate
 

Do we actually want to force the navigation in this case? If a URL is already open and in memory, it seems a bit of a waste to navigate to exactly the same URL.

WebAPKs force navigations in this case.

The bug here is that the notification wants to navigate to a different URL than the one that the webapp is currently showing. For instance, the user may be on the twitter home page and the notification may want to navigate to the twitter conversation view

The repro case you have seems to use the same URL being loaded as the notification wants to navigate to. Does it still repro if you are trying to go to a different URL? Or is it a sporadic behaviour?

Dominick, thank you for the question. Yes, it still repros if you are trying to go to a different URL. It repros both if the notification is
trying to go to a different URL than the current URL
trying to go to a different URL than the start URL

The bug is not sporadic.

Thanks for clarifying. I still think it's a negative experience if we navigate when we're already at the URL that was asked to be opened.

But then again, I suppose the default behaviour for deep link navigation is to always navigate, so perhaps that's also okay for notifications. It would be nice if we could find a smart way of telling when a page is or isn't stale, but I guess consistency with ordinary deep linking is desirable.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/aca98f1a90f13831326bb304c6baf83274134afa

commit aca98f1a90f13831326bb304c6baf83274134afa
Author: Peter Kotwicz <pkotwicz@chromium.org>
Date: Sat Jul 22 01:35:54 2017

[Android Webapp] Always navigate as a result of clients#openWindow()

This CL makes webapps always navigate as a result of
clients#openWindow()
In particular:
- The CL moves WebApkConstants#EXTRA_WEBAPK_FORCE_NAVIGATION to
ShortcutHelper
- Sets the extra in ServiceTabLauncher#launchTab() for webapps

BUG= 744843 
NOPRESUBMIT=true
(Because the version in shell_apk_version.gni does not need to
be incremented because although I renamed
WebApkConstants#EXTRA_WEBAPK_FORCE_NAVIGATION I did not change
its value)

Change-Id: I98465c1f8773a705dc7177792256d901bf9aa6bc
Reviewed-on: https://chromium-review.googlesource.com/575328
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Xi Han <hanxi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488831}
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/java/src/org/chromium/chrome/browser/ServiceTabLauncher.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/java/src/org/chromium/chrome/browser/ShortcutHelper.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebApkInfo.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebApkUpdateDataFetcher.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappInfo.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/javatests/src/org/chromium/chrome/browser/webapps/WebApkUpdateDataFetcherTest.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/javatests/src/org/chromium/chrome/browser/webapps/WebApkUpdateManagerTest.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/javatests/src/org/chromium/chrome/browser/webapps/WebappModeTest.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/javatests/src/org/chromium/chrome/browser/webapps/WebappVisibilityTest.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/junit/src/org/chromium/chrome/browser/webapps/WebApkInfoTest.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/junit/src/org/chromium/chrome/browser/webapps/WebApkUpdateManagerTest.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/junit/src/org/chromium/chrome/browser/webapps/WebappInfoTest.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/webapk/libs/client/src/org/chromium/webapk/lib/client/WebApkNavigationClient.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/webapk/libs/common/src/org/chromium/webapk/lib/common/WebApkConstants.java
[modify] https://crrev.com/aca98f1a90f13831326bb304c6baf83274134afa/chrome/android/webapk/shell_apk/src/org/chromium/webapk/shell_apk/MainActivity.java

Improved repro steps

Repro steps:
1) In chrome://flags disable "Improved Add to Homescreen"
2) Navigates to https://tests.peter.sh/notification-generator/
3) Tap "Add to Home screen" in the app menu
4) Close Chrome
5) Tap the newly added icon on the home screen. This should launch Chrome in fullscreen mode
6) Select "Only open a new window" in the Action <select> combo box
7) Tap the "Display the notification" <button> on the web page. This should generate a notification
8) Tap on the "Peter Beverloo" link
9) Tap on the notification

Expected:
The webapp navigates to https://tests.peter.sh/notification-generator/
Actual:
The webapp does not navigate