I think that the expected behavior is that the existing Chrome should have been launched without showing an error message.

Ah indeed, grt's right, not sure why there's an error than. Can someone test this with plain installers and then with Google Update installers? Maybe they do extra detection that we don't want them to?

I think I see the problem. The launch happens as desired, but setup.exe reports it as a failure rather than a success to GU.

ganesh: This is happening because Chrome's installer writes InstallerResult=1 (INSTALLER_RESULT_FAILED_CUSTOM_ERROR) in this case. I think the intent was for Chrome's installer to write 0 (INSTALLER_RESULT_SUCCESS). Changing this is simple enough. My question is: is this enough? In this case, Chrome will be telling GU via InstallerResult that the install succeeded, yet there will be no HKCU\...\Clients\{...}\pv in the registry since the per-user installer will have launched the existing per-machine Chrome. Can you tell how GU will handle this? The desire is for there to be no error UX from GU since Chrome's installer will launch Chrome for the user. Thanks.

 Issue 144864  has been merged into this issue.

I think Omaha would show the user an error if HKCU\...\Clients\{...}\pv is not written. How about writing a custom InstallerResultUIString that tells the user that Chrome is already installed for all users?

 Issue 104519  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/70c65451381988189ef8d591f581ac62653f2829

commit 70c65451381988189ef8d591f581ac62653f2829
Author: grt <grt@chromium.org>
Date: Tue Aug 23 19:19:27 2016

Provide a message to Google Update for the user when a system-level Chrome is already installed.

BUG= 625322 

Review-Url: https://codereview.chromium.org/2168703002
Cr-Commit-Position: refs/heads/master@{#413812}

[modify] https://crrev.com/70c65451381988189ef8d591f581ac62653f2829/chrome/app/chromium_strings.grd
[modify] https://crrev.com/70c65451381988189ef8d591f581ac62653f2829/chrome/app/google_chrome_strings.grd
[modify] https://crrev.com/70c65451381988189ef8d591f581ac62653f2829/chrome/installer/setup/setup_main.cc
[modify] https://crrev.com/70c65451381988189ef8d591f581ac62653f2829/chrome/installer/util/prebuild/create_string_rc.py

As Robert pondered in the code review, the new Chrome instance does indeed open over the GU dialog that says "Google Chrome is already installed for all users on your computer." I think this is an improvement over "The installer encountered error 3", and may be the right thing: the user was trying to install Chrome, and a Chrome window opened. Yes, they'll see a dialog behind it informing them that they already had Chrome. I'll work on having this message added to those listed in https://support.google.com/chrome/answer/6315198?hl=en&rd=1, which is what the "Help" button on that dialog leads the user to.

The new help text has gone live at https://support.google.com/chrome/answer/6315198. Calling this fixed.