Set up a field trial flag to prerender Instant search base url on omnibox focus event.

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 3cbd7d8c01d59765f49ef27c7e2253056c37bcae..bbc50c3b39be593499aafaeb231be5eae38c7fa0 100644
--- a/chrome/browser/search/search.h
+++ b/chrome/browser/search/search.h
@@ -162,10 +162,15 @@ std::vector<GURL> GetSearchURLs(Profile* profile);
 // trials.
 GURL GetSearchResultPrefetchBaseURL(Profile* profile);
 
-// Returns true if 'prefetch_results' flag is set to true in field trials to
-// prefetch high-confidence search suggestions.
+// Returns true if 'prerender_instant_url_on_omnibox_focus' flag is enabled in
+// field trials to prerender Instant search base page when the omnibox is
+// focused.
 bool ShouldPrefetchSearchResults();
 
+// Returns true if 'prerender_instant_url_on_omnibox_focus' flag is set to true
+// to prerender instant search base page on focusing omnibox.
+bool ShouldPrerenderInstantUrlOnOmniboxFocus();
+
 // Returns true if 'reuse_instant_search_base_page' flag is set to true in field
 // trials to reuse the prerendered page to commit any search query.
 bool ShouldReuseInstantSearchBasePage();