crash-reporter: Replace the crash_sender script by a service daemon.

BUG=chromium:391887
TEST=Integration tests
CQ-DEPEND=I02ce7593fcfae4ba1d7d3ebdf3912901e635f1c9
CQ-DEPEND=I00315ad47657cebd9e8a4a0121ecb54114a7e200

Change-Id: I2f4546c82fb3769b5f3da5d22949551412096b10
Reviewed-on: https://chromium-review.googlesource.com/208671


Tested-by: Benjamin Lerman <qsr@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>