Add general suggestion processor and migrate default suggestion

This patch adds a new interface to generalize the task of processing
new omnibox suggestions. Each implementor can specify a custom model
for the suggestion to be rendered in a custom view. As proof of
concept, the existing default omnibox suggestion has been migrated to
its own package and implements the new interface.

Bug:901952

Change-Id: I246ae64229ac6306f2a4a0bb38c46f5da637bd92
Reviewed-on: https://chromium-review.googlesource.com/c/1410011
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623011}
12 files changed