[Explore Sites] Adding GetIcon callback to fetch the favicon for a site.

This callback allows Java to fetch a favicon for a site from the native code.

Change-Id: Id4a8d86f68ade3b48e0f0dc937fa4b19c3ba8a50
Reviewed-on: https://chromium-review.googlesource.com/1241694
Commit-Queue: Jonathan Freed <freedjm@chromium.org>
Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594125}
4 files changed