Omnibox: Force text field to LTR context if it is a URL.

      This means that URLs will be displayed in a left-to-right paragraph
context. Right-to-left runs are still rendered RTL, but will not flip
the whole URL around. For example (if &quotABC&quot is Hebrew), this will render
&quotABC.com&quot as &quotCBA.com&quot, rather than &quotcom.CBA&quot.

This is consistent with the behaviour in the Omnibox drop-down items
(OmniboxResultView::CreateClassifiedRenderText) and status bubble
(StatusBubbleViews::SetURL).

BUG=495933,421332

Review URL: https://codereview.chromium.org/1189553002

Cr-Commit-Position: refs/heads/master@{#334537}