Gets the key value of 'name' to generate a valid list of sink names.

sink now contains more information than just name.
See https://chromium-review.googlesource.com/c/chromium/src/+/1637408.

Bug: 968849
Change-Id: Ib90fdc30b22dc26c695d0cc5b8fc9faab5e004b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1648889
Commit-Queue: Clifford Cheng <cliffordcheng@chromium.org>
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Auto-Submit: Clifford Cheng <cliffordcheng@chromium.org>
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667377}