Move TopSites preferences registration to history component
Move the registration of the TopSites preferences from TopSitesFactory
to TopSitesImpl so that it can be shared with iOS.
Move kNtpMostVisitedURLsBlacklist preference definition to the history
component as it is the sole client of that constant and rename it (but
do not change its value so that the user preference is not lost).
Change TopSitesImpl to use the constant kMostVisitedURLsBlacklist instead
of a variable passed via the constructor to access the preference.
BUG=479174
TBR=jochen
Review URL: https://codereview.chromium.org/
1192403002
Cr-Commit-Position: refs/heads/master@{#335478}