[MostLikely favicons] Decrease min_size to 0 and make params configurable

This CL changes the minimum size for fetching MostLikely favicons to 0
px. This means that we download even small icons and thus display a
colored tile instead of a gray tile.

Furthermore, the CL makes the min and desired sizes configurable by
field trial parameters to allow for more flexibility in experimenting /
launching.

Bug: 536988
Change-Id: I872243cc315b103eca9d30883f4c00026abe18eb
Reviewed-on: https://chromium-review.googlesource.com/567986
Commit-Queue: Jan Krcal <[email protected]>
Reviewed-by: Mikel Astiz <[email protected]>
Cr-Commit-Position: refs/heads/master@{#486356}
diff --git a/components/ntp_tiles/icon_cacher_impl.h b/components/ntp_tiles/icon_cacher_impl.h
index e15ceaf..671b020 100644
--- a/components/ntp_tiles/icon_cacher_impl.h
+++ b/components/ntp_tiles/icon_cacher_impl.h
@@ -52,6 +52,8 @@
       PopularSites::Site site,
       const base::Closure& icon_available,
       const base::Closure& preliminary_icon_available) override;
+
+  // TODO(jkrcal): Rename all instances of "MostLikely" to "ChromeSuggestions".
   void StartFetchMostLikely(const GURL& page_url,
                             const base::Closure& icon_available) override;