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

chrome/browser/search/search_unittest.cc

Index: chrome/browser/search/search_unittest.cc
diff --git a/chrome/browser/search/search_unittest.cc b/chrome/browser/search/search_unittest.cc
index 6e6b6dccd83494e4b0f1109e3797a2b72332f1ca..faf292067ad05c495779d6ba27415dd1828beabd 100644
--- a/chrome/browser/search/search_unittest.cc
+++ b/chrome/browser/search/search_unittest.cc
@@ -689,6 +689,24 @@ TEST_F(SearchTest, ShouldPrefetchSearchResults_EnabledViaFieldTrial) {
   EXPECT_EQ(80ul, EmbeddedSearchPageVersion());
 }
 
+TEST_F(SearchTest,
+       ShouldPrerenderInstantUrlOnOmniboxFocus_DisabledViaFieldTrial) {
+  ASSERT_TRUE(base::FieldTrialList::CreateFieldTrial(
+      "EmbeddedSearch",
+      "Group1 espv:89 prerender_instant_url_on_omnibox_focus:0"));
+  EXPECT_FALSE(ShouldPrerenderInstantUrlOnOmniboxFocus());
+  EXPECT_EQ(89ul, EmbeddedSearchPageVersion());
+}
+
+TEST_F(SearchTest,
+       ShouldPrerenderInstantUrlOnOmniboxFocus_EnabledViaFieldTrial) {
+  ASSERT_TRUE(base::FieldTrialList::CreateFieldTrial(
+      "EmbeddedSearch",
+      "Group1 espv:80 prerender_instant_url_on_omnibox_focus:1"));
+  EXPECT_TRUE(ShouldPrerenderInstantUrlOnOmniboxFocus());
+  EXPECT_EQ(80ul, EmbeddedSearchPageVersion());
+}
+
 TEST_F(SearchTest, ShouldPrefetchSearchResults_EnabledViaCommandLine) {
   CommandLine::ForCurrentProcess()->AppendSwitch(
       switches::kPrefetchSearchResults);