[Icons NTP] Enable Large Icon URL storage and image fetching (Touch Icons only), behind flag.
This works with crrev.com/1007563004 so URLs for Big Icons (currently only
Apple Touch Icon) are saved into Favicon database, and the icons get fetched
and stored. The feature is hidden behind flag "IconNTP/Enabled". rogerm@ is
working on bounding storage size of large icons.
Also doing some refactoring on FaviconHandler: existing has some ambiguity
on "handler type" and "icon type".
BUG=467712
Review URL: https://codereview.chromium.org/1010293002
Cr-Commit-Position: refs/heads/master@{#321140}
4 files changed
