split view: Fix split view drag indicators in multi-display dragging

Multi-display dragging was not accounted for in
https://chromium-review.googlesource.com/c/chromium/src/+/2039140

Test: ash_unittests All/SplitViewOverviewSessionInClamshellTestMultiDisplayOnly.MultiDisplayDragging/0
Bug: 961170
Change-Id: I9db1c280702e0197d24d4e18c8d4c7d441999061
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2055808
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741494}
2 files changed