[css-contain] Fix <select> dimensions when size containment is set

In r666210 we fixed the dimensions of <select> elements
with size containment.
However the fix was not covering the case when you set
"contain: size" to an already existent <select> element.

To fix this we need to reset the options width
in LayoutMenuList::UpdateOptionsWidth().

BUG=966673
TEST=external/wpt/css/css-contain/contain-size-select-002.html

Change-Id: I162134ff050d64e9ff1d824b5747adafb9a993c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1647152
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Commit-Queue: Manuel Rego <rego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#666594}
2 files changed