Restrict Instant field trial to UMA opt-in users.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 9a9fc6d258330a57d994dd0bd744544c96efd5bd..073b6aa16490d2d9de70d8bff53e8cc7b8b5aadf 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -279,10 +279,6 @@ const char kInstantEnabledOnce[] = "instant.enabled_once";
 // Time when instant was last enabled.
 const char kInstantEnabledTime[] = "instant.enabled_time";
 
-// Random number drawn and used by the Instant field trial. Stored in prefs to
-// provide a consistent field trial experience across browser restarts.
-const char kInstantFieldTrialRandomDraw[] = "instant.field_trial_random_draw";
-
 // Used to maintain instant promo keys. See PromoCounter for details of subkeys
 // that are used.
 const char kInstantPromo[] = "instant.promo";