Fix DesktopMediaPickerViews positioning

Before this change DesktopMediaPickerViews would center itself on the
page (and be spoofable), which is in conflict with it being a web-modal
dialog that normally attaches to the location bar.

This change also removes the close-x which is out of place for web-modal
dialogs (and redundant with the existing close button).

Bug: chromium:896012
Change-Id: I6d87a626cb5a4a3f2af87667faa3b2a718905202
Reviewed-on: https://chromium-review.googlesource.com/c/1284755
Commit-Queue: Peter Boström <pbos@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600572}
2 files changed