Add a new field trial for Instant.

chrome/browser/instant/instant_controller.h

 // Copyright (c) 2011 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.
 
 #ifndef CHROME_BROWSER_INSTANT_INSTANT_CONTROLLER_H_
 #define CHROME_BROWSER_INSTANT_INSTANT_CONTROLLER_H_
 #pragma once
 
 #include <set>
 #include <string>
@@ skipping 90 matching lines @@
   // false a commit does not result in committing the last url passed to update.
   // A return value of false happens if we're in the process of determining if
   // the page supports instant.
   bool IsCurrent();
 
   // Returns true if the caller should proceed with committing the preview. A
   // return value of false means that there is no valid preview to commit. This
   // is used by Browser, when the user presses <Enter>, to decide whether to
   // load the omnibox contents through Instant or otherwise. This is needed
   // because calls to |Update| don't necessarily result in a preview being
-  // shown, such as in the HIDDEN field trial.
+  // shown, such as in the HIDDEN and SILENT field trials.
   bool PrepareForCommit();
 
   // Invoked when the user does some gesture that should trigger making the
   // current previewed page the permanent page.  Returns the TCW that contains
   // the committed preview.
   TabContentsWrapper* CommitCurrentPreview(InstantCommitType type);
 
   // Sets InstantController so that when the mouse is released the preview is
   // committed.
   void SetCommitOnMouseUp();
@@ skipping 134 matching lines @@
   // The URL of the most recent match passed to |Update|.
   GURL last_url_;
 
   // The most recent user_text passed to |Update|.
   string16 last_user_text_;
 
   DISALLOW_COPY_AND_ASSIGN(InstantController);
 };
 
 #endif  // CHROME_BROWSER_INSTANT_INSTANT_CONTROLLER_H_