Get HistoryTabHelper to use GetContentSuggestionsReferrerURL instead of local constant.

Referrer that content suggestions navigations get annotated with is now
controlled by Finch experiment (crrev.com/c/1185857).
GetContentSuggestionsReferrerURL() should be used to retrieve its value.

BUG=916274

Change-Id: Ia64f1119b8952e2a8500d9e4a7d6a29fdef4c5f2
Reviewed-on: https://chromium-review.googlesource.com/c/1384937
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Pavel Yatsuk <pavely@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620844}
2 files changed