[omnibox] Add OmniboxUICuesForSearchHistoryMatches feature flag

This CL provides a feature flag that enables a small subset of
kOmniboxSuggestionTransparencyOptions.

It just enables the clock icon on search history matches.

Bug: 929477
Change-Id: I5aa112cd2627a25744ee00e70a735eed5892c0cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1579466
Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653368}
3 files changed