Add alignment.css ref to align-content-distribution tests

This CL:

* adds a required reference to the alignment.css resource file,
that provides alignment-related CSS classes used in several test cases.
Adding this reference fixes the align-content-distribution tests.

* changes the dimension of grids having 3 rows, .verticalLR and
.stretchedGrid classes, and gives them a new value of 300px width and
400px height (by using the class .width300height400).
This way each row width is now equal to 300px/3=100px, instead of
the previous dimension of 400px/3=133,33...px. The 133,33...px dimension
was, in fact, interpreted differently in different browsers,
thus making some tests fail in WebKit and Firefox.

* removes the -expected.txt files, related to align-content-distribution
tests, that were generated when these tests were failing.

Change-Id: I404dd188e8a2275042b4ace218c78a99e3248be5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1996303
Reviewed-by: Javier Fernandez <jfernandez@igalia.com>
Commit-Queue: Javier Fernandez <jfernandez@igalia.com>
Cr-Commit-Position: refs/heads/master@{#731689}
6 files changed