[blinkpy] Include trailing_comments in Expectation objects returned from TestExpectations.

This is part 2/2 of this change, the typ-side change is crrev.com/c/2040012

Change-Id: I4e3ee43399bfd7b3999db9e94e38bbc0adbf3442
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2039999
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Luke Z <lpz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740690}
2 files changed