Add event handler for cursor fallback mode

Bug: 907116
Change-Id: I0abff3ca6160380a6498f5d86a6460d9bcfba029
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504845
Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Jianpeng Chao <chaopeng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639350}
10 files changed