Fix fieldtrial_testing_config.json entry for reopen tab IPH

The enable_features array was missing in my last CL.

Bug: 887991
Change-Id: Ie69d9189a3255e93ee0fb41b24bc54db9b3d670a
Reviewed-on: https://chromium-review.googlesource.com/c/1489108
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635684}
1 file changed