I found it difficult to fix this by a simple fix without risk of affecting other parts. So I would like to punt this M-63 unless this is required for M61.
If this must be in M61, please assign fukino@ or someone else in the team.

> If this must be in M61, please assign fukino@ or someone else in the team.
Because I will be absent next week.

This is caused by not preventing the default behavior of dragging start event in the list container. Currently we do either:
- start drag selection
- start dragging selected file, including the case where we change selection right before drag start.

We'll need to add the third case where it simply prevents the default and do nothing.
https://chromium-review.googlesource.com/c/chromium/src/+/842583/2/ui/file_manager/file_manager/foreground/js/file_transfer_controller.js

> - start drag selection
For disambiguation, this means "to initiate the selection gesture by drawing the rectangular box to multiple select files by mouse drag".

Assigning to myself to investigate for M66.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/15d768df3adecd9d7b8d2b5f26e615e28b5184b0

commit 15d768df3adecd9d7b8d2b5f26e615e28b5184b0
Author: Sasha Morrissey <sashab@chromium.org>
Date: Tue Feb 20 09:11:01 2018

Deselect elements and cancel drag if initiated in files list padding

Deselect elements and cancel a touchscreen drag if the drag is initiated
in the files list padding area, below the list.

Bug:  760552 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I163ebe6c16f7295af3feb25c56a9abfd99d483fc
Reviewed-on: https://chromium-review.googlesource.com/923619
Reviewed-by: Naoki Fukino <fukino@chromium.org>
Commit-Queue: Sasha Morrissey <sashab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537743}
[modify] https://crrev.com/15d768df3adecd9d7b8d2b5f26e615e28b5184b0/ui/file_manager/file_manager/foreground/js/file_transfer_controller.js
[modify] https://crrev.com/15d768df3adecd9d7b8d2b5f26e615e28b5184b0/ui/file_manager/file_manager/foreground/js/ui/file_grid.js
[modify] https://crrev.com/15d768df3adecd9d7b8d2b5f26e615e28b5184b0/ui/file_manager/file_manager/foreground/js/ui/file_table.js