The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b9c3c20ba9a2a3c05b6d0f976e4a2d71c8a74fa6

commit b9c3c20ba9a2a3c05b6d0f976e4a2d71c8a74fa6
Author: pkl <pkl@chromium.org>
Date: Mon May 01 18:54:40 2017

Removes Native App Launcher functionality.

This is the first step of deprecating Native App Launcher. This step
removes the functionality from Chrome so testing can start.

There will be lots of dead code and unused classes/methods left after
this step and they will be pruned in subsequent CLs.

BUG= 711511 
TEST=Tools > Settings > Google Apps should not be there. Visits to Maps or YouTube sites will not show infobar. Tapping on Maps or YouTube links may still launch Maps and YouTube app because of Universal Links.

Review-Url: https://codereview.chromium.org/2821453003
Cr-Commit-Position: refs/heads/master@{#468374}

[modify] https://crrev.com/b9c3c20ba9a2a3c05b6d0f976e4a2d71c8a74fa6/ios/chrome/browser/tabs/tab.mm
[modify] https://crrev.com/b9c3c20ba9a2a3c05b6d0f976e4a2d71c8a74fa6/ios/chrome/browser/tabs/tab_unittest.mm
[modify] https://crrev.com/b9c3c20ba9a2a3c05b6d0f976e4a2d71c8a74fa6/ios/chrome/browser/ui/settings/settings_collection_view_controller.mm
[modify] https://crrev.com/b9c3c20ba9a2a3c05b6d0f976e4a2d71c8a74fa6/ios/chrome/browser/ui/settings/settings_egtest.mm

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/chrome/ios_internal.git/+/25baab43928eaebcc1610c5c06aebe48fdd079d9

commit 25baab43928eaebcc1610c5c06aebe48fdd079d9
Author: pkl <pkl@google.com>
Date: Mon May 01 23:53:30 2017

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/333f8780006c4409f44664bdc7d4637bfe636c35

commit 333f8780006c4409f44664bdc7d4637bfe636c35
Author: pkl <pkl@chromium.org>
Date: Tue May 02 22:53:21 2017

Revert of Removes Native App Launcher functionality. (patchset #4 id:60001 of https://codereview.chromium.org/2821453003/ )

Reason for revert:
Nothing's broken, but will reland with an
experimental flag.

Original issue's description:
> Removes Native App Launcher functionality.
>
> This is the first step of deprecating Native App Launcher. This step
> removes the functionality from Chrome so testing can start.
>
> There will be lots of dead code and unused classes/methods left after
> this step and they will be pruned in subsequent CLs.
>
> BUG= 711511 
> TEST=Tools > Settings > Google Apps should not be there. Visits to Maps or YouTube sites will not show infobar. Tapping on Maps or YouTube links may still launch Maps and YouTube app because of Universal Links.
>
> Review-Url: https://codereview.chromium.org/2821453003
> Cr-Commit-Position: refs/heads/master@{#468374}
> Committed: https://chromium.googlesource.com/chromium/src/+/b9c3c20ba9a2a3c05b6d0f976e4a2d71c8a74fa6

TBR=rohitrao@chromium.org,eugenebut@chromium.org,marq@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG= 711511 

Review-Url: https://codereview.chromium.org/2854883003
Cr-Commit-Position: refs/heads/master@{#468805}

[modify] https://crrev.com/333f8780006c4409f44664bdc7d4637bfe636c35/ios/chrome/browser/tabs/tab.mm
[modify] https://crrev.com/333f8780006c4409f44664bdc7d4637bfe636c35/ios/chrome/browser/tabs/tab_unittest.mm
[modify] https://crrev.com/333f8780006c4409f44664bdc7d4637bfe636c35/ios/chrome/browser/ui/settings/settings_collection_view_controller.mm
[modify] https://crrev.com/333f8780006c4409f44664bdc7d4637bfe636c35/ios/chrome/browser/ui/settings/settings_egtest.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/659aad38059a5877a7aa467212db0f9d9a5f5fcc

commit 659aad38059a5877a7aa467212db0f9d9a5f5fcc
Author: pkl <pkl@chromium.org>
Date: Wed May 03 23:57:59 2017

Disables Native App Launcher functionality.

This is the first step of deprecating Native App Launcher.
This puts the functionality behind an experimental flag
experimental_flags::IsNativeAppLauncherEnabled().
There will be lots of dead code and unused classes/methods left after
this step and they will be removed after experiment is removed.

Default for experiment is Native App Launcher *disabled*.

BUG= 711511 
TEST=Tools > Settings > Google Apps should not be there. Visits to Maps or YouTube sites will not show infobar. Tapping on Maps or YouTube links may still launch Maps and YouTube app because of Universal Links.

Review-Url: https://codereview.chromium.org/2860573003
Cr-Commit-Position: refs/heads/master@{#469207}

[modify] https://crrev.com/659aad38059a5877a7aa467212db0f9d9a5f5fcc/ios/chrome/browser/experimental_flags.h
[modify] https://crrev.com/659aad38059a5877a7aa467212db0f9d9a5f5fcc/ios/chrome/browser/experimental_flags.mm
[modify] https://crrev.com/659aad38059a5877a7aa467212db0f9d9a5f5fcc/ios/chrome/browser/resources/Settings.bundle/Experimental.plist
[modify] https://crrev.com/659aad38059a5877a7aa467212db0f9d9a5f5fcc/ios/chrome/browser/tabs/tab.mm
[modify] https://crrev.com/659aad38059a5877a7aa467212db0f9d9a5f5fcc/ios/chrome/browser/tabs/tab_unittest.mm
[modify] https://crrev.com/659aad38059a5877a7aa467212db0f9d9a5f5fcc/ios/chrome/browser/ui/settings/settings_collection_view_controller.mm
[modify] https://crrev.com/659aad38059a5877a7aa467212db0f9d9a5f5fcc/ios/chrome/browser/ui/settings/settings_egtest.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c899e16dcca08a6faabf99f3f283bcc01e6f44f9

commit c899e16dcca08a6faabf99f3f283bcc01e6f44f9
Author: pkl <pkl@chromium.org>
Date: Wed May 10 17:06:07 2017

Adds MailtoURLRewriterObserver to MailtoURLRewriter

Allows an observer to be notified of changes to the default mailto:
handler. This will be needed for implementation of Settings UI.

BUG= 711511 

Review-Url: https://codereview.chromium.org/2859743002
Cr-Commit-Position: refs/heads/master@{#470620}

[modify] https://crrev.com/c899e16dcca08a6faabf99f3f283bcc01e6f44f9/ios/chrome/browser/web/mailto_url_rewriter.h
[modify] https://crrev.com/c899e16dcca08a6faabf99f3f283bcc01e6f44f9/ios/chrome/browser/web/mailto_url_rewriter.mm
[modify] https://crrev.com/c899e16dcca08a6faabf99f3f283bcc01e6f44f9/ios/chrome/browser/web/mailto_url_rewriter_unittest.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/38f94f533d809b4202db39ac8c17be4442eb4256

commit 38f94f533d809b4202db39ac8c17be4442eb4256
Author: pkl <pkl@chromium.org>
Date: Fri May 12 19:53:11 2017

Adds Compose Email Settings UI for deprecating Native App Launcher

BUG= 711511 

Review-Url: https://codereview.chromium.org/2870783002
Cr-Commit-Position: refs/heads/master@{#471419}

[modify] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/app/strings/ios_strings.grd
[modify] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/ui/settings/BUILD.gn
[add] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/ui/settings/compose_email_handler_collection_view_controller.h
[add] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/ui/settings/compose_email_handler_collection_view_controller.mm
[add] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/ui/settings/compose_email_handler_collection_view_controller_unittest.mm
[modify] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/ui/settings/content_settings_collection_view_controller.h
[modify] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/ui/settings/content_settings_collection_view_controller.mm
[modify] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/ui/settings/content_settings_collection_view_controller_unittest.mm
[modify] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/web/BUILD.gn
[add] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/web/fake_mailto_handler_helpers.h
[add] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/web/fake_mailto_handler_helpers.mm
[modify] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/web/mailto_url_rewriter.h
[modify] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/web/mailto_url_rewriter.mm
[modify] https://crrev.com/38f94f533d809b4202db39ac8c17be4442eb4256/ios/chrome/browser/web/mailto_url_rewriter_unittest.mm

Verified on latest chrome canary version 60.0.3100.0 on iPhone 6s plus with iOS 10.3.1, iPad Air 10.2.1, following the steps mentioned in comment #9. Google Apps feature is removed.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d60b42a00189e71d3a72c3c1ee079c1f269c1fef

commit d60b42a00189e71d3a72c3c1ee079c1f269c1fef
Author: pkl <pkl@chromium.org>
Date: Mon May 22 20:40:15 2017

Show all mailto: handlers, but dim unavailable ones.

Based on updated design doc, Compose Email settings should always be
shown even if there is only one Mail client app installed. The settings
screen should show all but dim the unavailable ones.

BUG= 711511 
TEST=Delete one or both of Mail and Gmail app and verify the Settings dialog. Check VoiceOver usage as well.

Review-Url: https://codereview.chromium.org/2889183005
Cr-Commit-Position: refs/heads/master@{#473681}

[modify] https://crrev.com/d60b42a00189e71d3a72c3c1ee079c1f269c1fef/ios/chrome/browser/ui/settings/compose_email_handler_collection_view_controller.mm
[modify] https://crrev.com/d60b42a00189e71d3a72c3c1ee079c1f269c1fef/ios/chrome/browser/ui/settings/compose_email_handler_collection_view_controller_unittest.mm
[modify] https://crrev.com/d60b42a00189e71d3a72c3c1ee079c1f269c1fef/ios/chrome/browser/ui/settings/content_settings_collection_view_controller.mm
[modify] https://crrev.com/d60b42a00189e71d3a72c3c1ee079c1f269c1fef/ios/chrome/browser/ui/settings/content_settings_collection_view_controller_unittest.mm
[modify] https://crrev.com/d60b42a00189e71d3a72c3c1ee079c1f269c1fef/ios/chrome/browser/web/fake_mailto_handler_helpers.h
[modify] https://crrev.com/d60b42a00189e71d3a72c3c1ee079c1f269c1fef/ios/chrome/browser/web/fake_mailto_handler_helpers.mm
[modify] https://crrev.com/d60b42a00189e71d3a72c3c1ee079c1f269c1fef/ios/chrome/browser/web/mailto_url_rewriter.mm

Verified on canary chrome 60.0.3108.0 on iPhone 6 plus (10.3.1) and iPAD Air(10.2.1) 

Followed the below steps
1. Launch chrome and load URL: http://tinyurl.com/SUMNE
2. Tap on "Send Email"

Observed: 
2.1: If gmail is installed, the Gmail will open
2.2: If gmail is not installed then the iOS mail app will open
2.3: If both not exist then a Restore "mail" pop up is displayed

Hi Peter,
In the CL linked in comment #22 a design doc is referenced, can you please link to that here?
Thanks,

https://docs.google.com/document/d/1Nd2VXSq5G8j4lu9Q0sY7ySxvvNNS5sCOOmmwasuyin4/edit