WebUI Omnibox Popup: Fix row width to not go outside the bounds.

  - Don't pass width=INT_MAX to
    render_widget_host_view->EnableAutoResize()
  - Add a 'max-width: 100vw' on the frontend side to prevent a somewhat
    inexplicable horizontal scrollbar.

Bug: b/447646130
Change-Id: I0e0e26c98100a7d618647d64a2b3a05c25850692
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6997935
Reviewed-by: David Yeung <dayeung@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1522951}