The following revision refers to this bug:
  https://chrome-internal.googlesource.com/chrome/ios_internal.git/+/18bbc2f37e479e3fe61b0e69c0450a2ffb48b20b

commit 18bbc2f37e479e3fe61b0e69c0450a2ffb48b20b
Author: jif <jif@google.com>
Date: Tue Sep 20 15:09:54 2016

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e9171baf955613633d96be5c327010f011549e63

commit e9171baf955613633d96be5c327010f011549e63
Author: jif <jif@chromium.org>
Date: Tue Sep 20 19:00:03 2016

Enable Spotlight Actions by default.

Matching downstream CL: https://chromereviews.googleplex.com/503587014/
Launch bug: https://bugs.chromium.org/p/chromium/issues/detail?id=647310

BUG= 648529 

Review-Url: https://codereview.chromium.org/2355743004
Cr-Commit-Position: refs/heads/master@{#419832}

[modify] https://crrev.com/e9171baf955613633d96be5c327010f011549e63/ios/chrome/browser/about_flags.mm
[modify] https://crrev.com/e9171baf955613633d96be5c327010f011549e63/ios/chrome/browser/experimental_flags.mm

We can remove the experimental flag altogether

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e09adff42771476c2e08d460439f18c8e0e531d1

commit e09adff42771476c2e08d460439f18c8e0e531d1
Author: jif <jif@chromium.org>
Date: Tue Feb 21 15:04:10 2017

Remove SpotlightActions experimental flag.

BUG= 648529 

Review-Url: https://codereview.chromium.org/2709793002
Cr-Commit-Position: refs/heads/master@{#451763}

[modify] https://crrev.com/e09adff42771476c2e08d460439f18c8e0e531d1/ios/chrome/app/application_delegate/user_activity_handler.mm
[modify] https://crrev.com/e09adff42771476c2e08d460439f18c8e0e531d1/ios/chrome/app/spotlight/actions_spotlight_manager.mm
[modify] https://crrev.com/e09adff42771476c2e08d460439f18c8e0e531d1/ios/chrome/browser/about_flags.mm
[modify] https://crrev.com/e09adff42771476c2e08d460439f18c8e0e531d1/ios/chrome/browser/chrome_switches.cc
[modify] https://crrev.com/e09adff42771476c2e08d460439f18c8e0e531d1/ios/chrome/browser/chrome_switches.h
[modify] https://crrev.com/e09adff42771476c2e08d460439f18c8e0e531d1/ios/chrome/browser/experimental_flags.h
[modify] https://crrev.com/e09adff42771476c2e08d460439f18c8e0e531d1/ios/chrome/browser/experimental_flags.mm
[modify] https://crrev.com/e09adff42771476c2e08d460439f18c8e0e531d1/ios/chrome/browser/resources/Settings.bundle/Experimental.plist

Verified the issue on the latest build 58.0.3026.0 canary tested on iPhone 7+(iOS 10).
Spotlight is on by default,works fine.