Omnibox: Suggestion Transparency Options - Add Clock vector icon

This CL adds the clock vector icon, but does not actually use it yet.

The clock icon may be used to represent personalized suggestions
sourced from a user's Search History. This is intended to better inform
the user where the suggestion came from.

This clock icon is sourced from the manually tweaked version from Joel
previously used as answer_when_is.icon, but recently removed.

This CL adds it back as clock.icon.

Bug: 929477
Change-Id: I54fd62057f15a67bf35af48d6cf8cbec2d4b35b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1553912
Commit-Queue: Tommy Li <tommycli@chromium.org>
Reviewed-by: Orin Jaworski <orinj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#650042}