Adds --merged-only command line option
Adds --merged-only command line option

Adds status:merged to gerrit filter.

Bug: 878433
Change-Id: Ica081fa0cd0e8a267ec0a8d711f749b4e91faec5
Reviewed-on: https://chromium-review.googlesource.com/1194310
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>
Commit-Queue: Peter Lee <d5a22bfb414d683c522ae986cbba00d025bb0a72@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools