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

chrome/browser/search/search.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/search/search.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
@@ skipping 48 matching lines @@
 const uint64 kEmbeddedPageVersionDefault = 1;
 // Use this variant to enable EmbeddedSearch SearchBox API in the results page.
 const uint64 kEmbeddedSearchEnabledVersion = 2;
 #else
 const uint64 kEmbeddedPageVersionDefault = 2;
 #endif
 
 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.
 const char kReuseInstantSearchBasePage[] = "reuse_instant_search_base_page";
 
 const char kDisplaySearchButtonFlagName[] = "display_search_button";
 const char kOriginChipFlagName[] = "origin_chip";
 #if !defined(OS_IOS) && !defined(OS_ANDROID)
 const char kEnableQueryExtractionFlagName[] = "query_extraction";
 #endif
@@ skipping 480 matching lines @@
 GURL GetNewTabPageURL(Profile* profile) {
   return NewTabURLDetails::ForProfile(profile).url;
 }
 
 GURL GetSearchResultPrefetchBaseURL(Profile* profile) {
   return ShouldPrefetchSearchResults() ?
       GetInstantURL(profile, kDisableStartMargin, true) : GURL();
 }
 
 bool ShouldPrefetchSearchResults() {
+  if (!IsInstantExtendedAPIEnabled())
+    return false;
+
   if (CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kPrefetchSearchResults)) {
     return true;
   }
 
   FieldTrialFlags flags;
   return GetFieldTrialInfo(&flags) && GetBoolValueForFlagWithDefault(
       kPrefetchSearchResultsFlagName, false, flags);
 }
 
-bool ShouldReuseInstantSearchBasePage() {
-  if (CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kPrefetchSearchResults)) {
-    return true;
-  }
-
+bool ShouldPrerenderInstantUrlOnOmniboxFocus() {
   if (!ShouldPrefetchSearchResults())
     return false;
 
+  FieldTrialFlags flags;
+  return GetFieldTrialInfo(&flags) && GetBoolValueForFlagWithDefault(
+      kPrerenderInstantUrlOnOmniboxFocus, false, flags);
+}
+
+bool ShouldReuseInstantSearchBasePage() {
+  if (!ShouldPrefetchSearchResults())
+    return false;
+
   FieldTrialFlags flags;
   return GetFieldTrialInfo(&flags) && GetBoolValueForFlagWithDefault(
       kReuseInstantSearchBasePage, false, flags);
 }
 
 GURL GetLocalInstantURL(Profile* profile) {
   return GURL(chrome::kChromeSearchLocalNtpUrl);
 }
 
 bool ShouldHideTopVerbatimMatch() {
@@ skipping 212 matching lines @@
 
 // Given a FieldTrialFlags object, returns the boolean value of the provided
 // flag.
 bool GetBoolValueForFlagWithDefault(const std::string& flag,
                                     bool default_value,
                                     const FieldTrialFlags& flags) {
   return !!GetUInt64ValueForFlagWithDefault(flag, default_value ? 1 : 0, flags);
 }
 
 }  // namespace chrome