Fixes possible crash in TableView

Fixes possible crash in TableView

The sequence leading to the crash is:
. Enable sorting.
. Have more than one selected row.
. Remove one of the selected rows. The removed row must also contain
  the anchor.
. Focus the table.

The crash happened because we tried to get the view index for -1.

In general the anchor shouldn't be -1 if there is at least one item in
the selection. The only place anchor could be -1 and there is a
selection is during removal. This patch fixes that.

BUG=480296
TEST=covered by test now.
R=sadrul@chromium.org

Committed: https://crrev.com/def5587881b9878e1b8bb6491db2fc977a7e76f3
Cr-Commit-Position: refs/heads/master@{#329853}

[sadrul, 2015-05-14 07:59:24]

lgtm

[sky, 2015-05-14 15:06:59]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2015-05-14 15:07:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1129233006/1

[commit-bot: I haz the power, 2015-05-14 15:11:01]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-14 15:11:54]

Patchset 1 (id:??) landed as
https://crrev.com/def5587881b9878e1b8bb6491db2fc977a7e76f3
Cr-Commit-Position: refs/heads/master@{#329853}