app: call Start on darwin
app: call Start on darwin

Still working on how/when to call Stop.

Change-Id: Ice56c4c71ba351765657bb86dc01649c8238859e
Reviewed-on: https://go-review.googlesource.com/1885
Reviewed-by: Hyang-Ah Hana Kim <d7e82c3c07f92613bcbf9a1e88f6b96c13caa3b0@gmail.com>

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