Android omnibox: Force paragraph direction to LTR.

This means that URLs will always be displayed in a left-to-right
context. Right-to-left runs are still rendered as RTL, but will not
cause the whole URL to flip around.

This fixes several spoofing concerns and makes Android's omnibox
consistent with the Views omnibox.

BUG=609680

Review-Url: https://codereview.chromium.org/1988553002
Cr-Commit-Position: refs/heads/master@{#400359}