App launcher: Added Finch experiment for the search ranking algorithm.

ui/app_list/search/mixer.h

 // Copyright 2013 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 UI_APP_LIST_SEARCH_MIXER_H_
 #define UI_APP_LIST_SEARCH_MIXER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 17 matching lines @@
 // result. The search controller can specify any number of groups, each with a
 // different number of results and priority boost. The "omnibox" group is
 // expected to contain omnibox results, and will be treated specially.
 class APP_LIST_EXPORT Mixer {
  public:
   explicit Mixer(AppListModel::SearchResults* ui_results);
   ~Mixer();
 
   // Adds a new mixer group. A maximum of |max_results| results will be
   // displayed from this group (if 0, will allow unlimited results from this
-  // group). Each result in the group will have its score boosted by |boost|.
+  // group). Behaviour depends on the AppListMixer field trial:
+  // - If default: Each result in the group will have its score boosted by
+  //   |boost|. |multiplier| is ignored.
+  // - If "Blended": |max_results| is a "soft" maximum; if there aren't enough
+  //   results from all groups, more than |max_results| may be chosen from this
+  //   group. Each result in the group will have its score multiplied by
+  //   |multiplier|. |boost| is ignored.
   // Returns the group's group_id.
-  size_t AddGroup(size_t max_results, double boost);
+  size_t AddGroup(size_t max_results, double boost, double multiplier);
 
   // Adds a new mixer group for the special "omnibox" group. This group will be
   // treated specially by the Mixer (it will be truncated such that it fills the
   // remaining slots without overflowing, but with at least one result). A
   // maximum of one group should be added using this method.
-  size_t AddOmniboxGroup(size_t max_results, double boost);
+  size_t AddOmniboxGroup(size_t max_results, double boost, double multiplier);
 
   // Associates a provider with a mixer group.
   void AddProviderToGroup(size_t group_id, SearchProvider* provider);
 
   // Collects the results, sorts and publishes them.
   void MixAndPublish(bool is_voice_query, const KnownResults& known_results);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(test::MixerTest, Publish);
 
@@ skipping 23 matching lines @@
   // NOTE: This is not necessarily the one with the highest *score*, as
   // |results| may not have been sorted yet.
   static void RemoveDuplicates(SortedResults* results);
 
   void FetchResults(bool is_voice_query, const KnownResults& known_results);
 
   AppListModel::SearchResults* ui_results_;  // Not owned.
   Groups groups_;
 
   // The ID of the omnibox group. The group with this ID will be treated
-  // specially by the Mixer.
-  // TODO(mgiuca): Omnibox group should not be treated specially.
+  // specially by the Mixer. Ignored if the AppListMixer field trial is
+  // "Blended".
+  // TODO(mgiuca): Remove this after the field trial is complete.
   size_t omnibox_group_ = 0;
   // Whether |omnibox_group_| has been set.
   bool has_omnibox_group_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(Mixer);
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_SEARCH_MIXER_H_