Don't do field trials if Instant is explicitly enabled.

chrome/browser/instant/instant_field_trial.cc

 // Copyright (c) 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/instant/instant_field_trial.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "chrome/browser/metrics/metrics_service.h"
 #include "chrome/browser/prefs/pref_service.h"
@@ skipping 48 matching lines @@
       return SILENT;
     if (switch_value == switches::kInstantFieldTrialControl)
       return CONTROL;
     return INACTIVE;
   }
 
   const int group = base::FieldTrialList::FindValue("Instant");
   if (group == base::FieldTrial::kNotFinalized || group == g_inactive)
     return INACTIVE;
 
+  // If Instant is already enabled explicitly, then it's not a field trial.
+  const PrefService* prefs = profile ? profile->GetPrefs() : NULL;
+  if (prefs && prefs->GetBoolean(prefs::kInstantEnabled))
+    return INACTIVE;
+
   // CONTROL and SILENT are unconstrained.
   if (group == g_control)
     return CONTROL;
   if (group == g_silent)
     return SILENT;
 
   // HIDDEN, SUGGEST and INSTANT need non-incognito, suggest-enabled profiles.
-  const PrefService* prefs = profile ? profile->GetPrefs() : NULL;
   if (!prefs || profile->IsOffTheRecord() ||
       !prefs->GetBoolean(prefs::kSearchSuggestEnabled)) {
     return INACTIVE;
   }
 
   if (group == g_hidden)
     return HIDDEN;
 
   // SUGGEST and INSTANT require UMA opt-in.
   if (!MetricsServiceHelper::IsMetricsReportingEnabled())
@@ skipping 62 matching lines @@
 
   NOTREACHED();
   return std::string();
 }
 
 // static
 bool InstantFieldTrial::ShouldSetSuggestedText(Profile* profile) {
   Group group = GetGroup(profile);
   return group != HIDDEN && group != SILENT;
 }