Add unit tests for TabGridItemTouchHelperCallback

Bug: 978236
Change-Id: If2bd37ed4182597e7ee0175f367604b9ec2bca42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674669
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Yue Zhang <yuezhanggg@google.com>
Cr-Commit-Position: refs/heads/master@{#672155}
2 files changed