Don't clear selection when spatial navigation moves focus

We kept a Selection.Clear() to not break the test "snav-textarea.html".

<textarea>'s behavior is the same, no matter whether
--enable-spatial-navigation is used or not, so instead of clearing
the <textarea>'s selection we just need to adapt the test.

This is a step towards our goal of simplifying the spatial navigation code.

Bug: 734552, 770147
Change-Id: If82c99658e44aee776afa87af823e005259415e0
Reviewed-on: https://chromium-review.googlesource.com/695103
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Takayoshi Kochi <kochi@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Commit-Queue: Hugo Holgersson <hugoh@vewd.com>
Cr-Commit-Position: refs/heads/master@{#506010}
3 files changed