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

chrome/browser/search/search.cc

Index: chrome/browser/search/search.cc
diff --git a/chrome/browser/search/search.cc b/chrome/browser/search/search.cc
index 7e01ef48eea42ccba507c17d2dc1b34247d769fa..ee558460b554e253a54212c71f974faa7b74c8a8 100644
--- a/chrome/browser/search/search.cc
+++ b/chrome/browser/search/search.cc
@@ -66,6 +66,8 @@ const uint64 kEmbeddedPageVersionDefault = 2;
 const char kHideVerbatimFlagName[] = "hide_verbatim";
 const char kPrefetchSearchResultsFlagName[] = "prefetch_results";
 const char kPrefetchSearchResultsOnSRP[] = "prefetch_results_srp";
+const char kPrerenderInstantUrlOnOmniboxFocus[] =
+    "prerender_instant_url_on_omnibox_focus";
 
 // Controls whether to reuse prerendered Instant Search base page to commit any
 // search query.
@@ -576,6 +578,15 @@ bool ShouldPrefetchSearchResults() {
       kPrefetchSearchResultsFlagName, false, flags);
 }
 
+bool ShouldPrerenderInstantUrlOnOmniboxFocus() {

[kmadhusu, 2014/06/13 00:40:28]

On Android Chrome, Embedded Search API is not enabled for all users. Therefore,
it's better to add the following check before reading the field trial flags:
  if (!IsInstantExtendedAPIEnabled())
    return false;

Sorry I missed this during the previous review.

[sidharthms, 2014/06/13 17:46:43]

Done.

+  if (!ShouldPrefetchSearchResults())
+    return false;
+
+  FieldTrialFlags flags;
+  return GetFieldTrialInfo(&flags) && GetBoolValueForFlagWithDefault(
+      kPrerenderInstantUrlOnOmniboxFocus, false, flags);
+}
+
 bool ShouldReuseInstantSearchBasePage() {
   if (CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kPrefetchSearchResults)) {