If I recall, this change happened because we made the NTP a modal dialog. I'm not sure how hard this would be to do with the new NTP. @Theresa do you know?

However, one thing I might imagine is that since the NTP is modal, you would lose the ability to go forward from the NTP if you tapped back too many times which could be bad.

+mdjones@ Since he's worked with some of the back-press logic.

Chrome goes to the background because there's nothing in the navigation history to go back to and ChromeTabbedActivity's logic in handleBackPressed() determines that we should minimize the app rather than closing the tab.

We don't currently track tabs opened from the option menu/new tab button separately from tabs opened via push notifications, keyboard shortcuts or other Chrome UI surfaces, though, so we may need a new TabLaunchType. But we should be able to do something in ChromeTabbedActivity#handleBackPressed() if we want to change the behavior.

The main trade off I see is that the user can't go forward when hitting the NTP and may end up closing the tab (and removing all the history). However, I suspect this is a rare case so I'm fine with returning to the NTP. @Chris - do you have any thoughts here?

Alternatively we can bring up Chrome Home to half height on the current page without going back to the full NTP Chrome Home.

In this case my expectation was that the tab would close. That's what happens on intents from other apps or when opening pages in a new tab. Which is why I would expect to go back to the NTP-over-tab-switcher state (i.e. preferring #c3 tp #c4)

Closing the tab would be a change from today's behavior so I'd be a little more cautious about that. Many people use back repeatedly to close Chrome and we have no been closing their tab when they do so, meaning changing this behavior may be surprising. I'm not against the idea though.

 Issue 736810  has been merged into this issue.

Ah yes - adding comment in.

We have been receiving feedback reports about users thinking their back button was broken by closing the app.

When the user navigates to a page from the NTP and taps back, we should go back to the NTP. Ideally, if the user taps back again, we can then close the app (to preserve the old behavior).

Ted, Kingston and I discussed this offline. A simple(ish) v1 approach would be to open the bottom sheet over the current tab instead of minimizing the app; if the user presses back again we would close the bottom sheet and a minimize the app. We can use TabLaunchType.FROM_CHROME_UI to determine when open the bottom sheet over the current tab; we need new tracking (probably in bottom sheet) to determine when to minimize the app on a successive back press.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f9a5bc602e1637160708dc1b7f168e777fc2b7ae

commit f9a5bc602e1637160708dc1b7f168e777fc2b7ae
Author: Matthew Jones <mdjones@chromium.org>
Date: Fri Jul 07 16:23:58 2017

[Home] Back button opens sheet if back navigation impossible

If a tab is created via Chrome's UI, hitting the back button will
eventually expand the bottom sheet before sending Chrome to the
background. Tests for the intended behaviors have been added as
well.

BUG= 732833 

Change-Id: I8d8308dcb7e21d1ee49fa3ab439cf7387c78f86b
Reviewed-on: https://chromium-review.googlesource.com/550929
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#484945}
[modify] https://crrev.com/f9a5bc602e1637160708dc1b7f168e777fc2b7ae/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
[modify] https://crrev.com/f9a5bc602e1637160708dc1b7f168e777fc2b7ae/chrome/android/java/src/org/chromium/chrome/browser/widget/bottomsheet/BottomSheet.java
[modify] https://crrev.com/f9a5bc602e1637160708dc1b7f168e777fc2b7ae/chrome/android/java_sources.gni
[add] https://crrev.com/f9a5bc602e1637160708dc1b7f168e777fc2b7ae/chrome/android/javatests/src/org/chromium/chrome/browser/widget/bottomsheet/BottomSheetBackBehaviorTest.java

Marking as fixed, we can discuss followups to this in a different bug.