InstantExtended: add a finch flag to disable Instant Extended on SRP.

chrome/browser/search/search.h

Index: chrome/browser/search/search.h
diff --git a/chrome/browser/search/search.h b/chrome/browser/search/search.h
index 716fa950bcad0e75f8f9309acadd3718d56e0e11..122f03c4674385bd9102832c325cee70e151bf43 100644
--- a/chrome/browser/search/search.h
+++ b/chrome/browser/search/search.h
@@ -137,6 +137,10 @@ bool ShouldShowInstantNTP();
 // field trials.
 bool ShouldShowRecentTabsOnNTP();
 
+// Returns true if Instant Extended should be disabled on the search results
+// page.
+bool ShouldSuppressInstantExtendedOnSRP();
+
 // Returns true if |my_url| matches |other_url|.
 bool MatchesOriginAndPath(const GURL& my_url, const GURL& other_url);