GitLab

- Removed unused methods
- Add ForTest for testing methods
- Unified SharingMessageHandler creation

Bug: 1015826
Change-Id: I99c8e1ea600969bd4bf2df4a648fb4c7746bc4d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1868958
Commit-Queue: Alex Chau <alexchau@chromium.org>
Reviewed-by: Richard Knoll <knollr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707400}