Introduce dynamic ablation of AutocompleteProviders using AC dynamic trials.

chrome/browser/autocomplete/autocomplete_field_trial.h

 // 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.
 
 #ifndef CHROME_BROWSER_AUTOCOMPLETE_AUTOCOMPLETE_FIELD_TRIAL_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_AUTOCOMPLETE_FIELD_TRIAL_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 
 // This class manages the Autocomplete field trials.
 class AutocompleteFieldTrial {
  public:
   // Creates the static field trial groups.
   // *** MUST NOT BE CALLED MORE THAN ONCE. ***
   static void ActivateStaticTrials();
 
   // Activates all dynamic field trials.  The main difference between
   // the autocomplete dynamic and static field trials is that the former
   // don't require any code changes on the Chrome side as they are controlled
   // on the server side.  Chrome binary simply propagates all necessary
   // information through the X-Chrome-Variations header.
   // This method, unlike ActivateStaticTrials(), may be called multiple times.
   static void ActivateDynamicTrials();
 
+  // Returns a bitmap containing AutocompleteProvider::Type values
+  // that should be disabled in AutocompleteController.
+  // This method simply goes over all autocomplete dynamic field trial groups
+  // and looks for group names like "ProvidersDisabled_NNN" where NNN is
+  // an integer corresponding to a bitmap mask.  All extracted bitmaps
+  // are OR-ed together and returned as the final result.
+  static int GetDisabledProviderTypes();
+
   // ---------------------------------------------------------
   // For the inline History Quick Provider field trial.
 
   // Returns whether the user is in any field trial group for this
   // field trial.  False indicates that the field trial wasn't
   // successfully created for some reason.
   static bool InDisallowInlineHQPFieldTrial();
 
   // Returns whether the user should get the experiment setup or
   // the default setup for this field trial.  The experiment
@@ skipping 83 matching lines @@
 
   // Returns whether HistoryQuick provider should allow breaking the
   // omnibox input string at cursor position.
   static bool InHQPUseCursorPositionFieldTrialExperimentGroup();
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(AutocompleteFieldTrial);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_AUTOCOMPLETE_FIELD_TRIAL_H_