Make display_ResolutionList run on both M37 and M38

The DisplayMode dict in Chrome is changed in M38. This CL makes sure the test
can run on both M37 (before the API change) and M38.

BUG=chromium:391681
TEST=manually run the test on link and pi and see them passed.

Change-Id: I791b8d3275098981ae6946d1d6df901a0346aa5a
Reviewed-on: https://chromium-review.googlesource.com/212612
Reviewed-by: Wai-Hong Tam <waihong@chromium.org>
Commit-Queue: Ting-Yuan Cheng <tingyuan@chromium.org>
Tested-by: Ting-Yuan Cheng <tingyuan@chromium.org>
4 files changed