[ios] Creates ImportDataMultilineDetailItem.

The ImportDataMultilineDetailCell was previously using
SettingsDetailItem as its model class, but items and cells should be 1:1
wherever possible.  This CL creates a new item class that's specific to
ImportDataMultilineDetailCell.

BUG=805213
TEST=None

Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I56d45bda5022b14214b43b0567e81ff82d5eef25
Reviewed-on: https://chromium-review.googlesource.com/1128608
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573352}
6 files changed