Provide experimental contextual suggestions when current URL comes from a google domain.

The counts for the Omnibox.ZeroSuggestRequests historgram are 35% smaller for groups that are running under the ZeroSuggestRedirectToChrome flag. Note that previous to this CL, a request was not made when the user was visiting an HTTPS page and the domain of the current was different from that of the service providing zero suggestions. This CL addresses this restrictions by making sure that requests are sent to the experimental service when Google is the default search engine AND the same request was validated to be sent to Google.

BUG=692471

Review-Url: https://codereview.chromium.org/2915163003
Cr-Commit-Position: refs/heads/master@{#476786}
void ZeroSuggestProvider::ResetSession() {
  set_field_trial_triggered(false);
}

void ZeroSuggestProvider::ResetSession() {
  set_field_trial_triggered(false);
}
