Allow controlling the Instant field trial through a command line flag.

chrome/browser/metrics/metrics_service_uitest.cc

Index: chrome/browser/metrics/metrics_service_uitest.cc
diff --git a/chrome/browser/metrics/metrics_service_uitest.cc b/chrome/browser/metrics/metrics_service_uitest.cc
index f323fdc5016518e6b95a0e5f93682db4311174a8..20fca2bd9622f63b7939cd7b8a92919771611912 100644
--- a/chrome/browser/metrics/metrics_service_uitest.cc
+++ b/chrome/browser/metrics/metrics_service_uitest.cc
@@ -39,11 +39,6 @@ class MetricsServiceTest : public UITest {
     scoped_refptr<BrowserProxy> window = automation()->GetBrowserWindow(0);
     ASSERT_TRUE(window.get());
 
-    // The Instant field trial causes a preload of the default search engine,
-    // which messes up the expected page load count. Setting this preference
-    // disables the field trial.
-    ASSERT_TRUE(window->SetBooleanPreference(prefs::kInstantEnabledOnce, true));
-
     FilePath page1_path;
     ASSERT_TRUE(PathService::Get(chrome::DIR_TEST_DATA, &page1_path));
     page1_path = page1_path.AppendASCII("title2.html");