Chameleon: Add a new display_SuspendStress test.

Create a new suspend/resume stress test, which tests external display functions
with DUT being repeatedly suspended and resumed.

BUG=chromium:358925
TEST=manually run the test on peppy and see it passed.

Change-Id: Ib73dbc327401a5040094488c1b859535339bb5a7
Reviewed-on: https://chromium-review.googlesource.com/207499
Reviewed-by: Hung-ying Tyan <tyanh@chromium.org>
Commit-Queue: Ting-Yuan Cheng <tingyuan@chromium.org>
Tested-by: Ting-Yuan Cheng <tingyuan@chromium.org>
5 files changed