app_list: Refactor mixer groups to avoid hard-coded groups in Mixer.

ui/app_list/search_controller.cc

 // 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.
 
 #include "ui/app_list/search_controller.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 15 matching lines @@
 namespace app_list {
 
 SearchController::SearchController(SearchBoxModel* search_box,
                                    AppListModel::SearchResults* results,
                                    History* history)
     : search_box_(search_box),
       dispatching_query_(false),
       mixer_(new Mixer(results)),
       history_(history),
       is_voice_query_(false) {
-  mixer_->Init();
 }
 
 SearchController::~SearchController() {
 }
 
 void SearchController::Start(bool is_voice_query) {
   Stop();
 
   base::string16 query;
   base::TrimWhitespace(search_box_->text(), base::TRIM_ALL, &query);
@@ skipping 38 matching lines @@
   }
 }
 
 void SearchController::InvokeResultAction(SearchResult* result,
                                           int action_index,
                                           int event_flags) {
   // TODO(xiyuan): Hook up with user learning.
   result->InvokeAction(action_index, event_flags);
 }
 
-void SearchController::AddProvider(Mixer::GroupId group,
+size_t SearchController::AddGroup(size_t max_results, double boost) {
+  return mixer_->AddGroup(max_results, boost);
+}
+
+void SearchController::AddProvider(size_t group_id,
                                    scoped_ptr<SearchProvider> provider) {
   provider->set_result_changed_callback(base::Bind(
       &SearchController::OnResultsChanged,
       base::Unretained(this)));
-  mixer_->AddProviderToGroup(group, provider.get());
+  mixer_->AddProviderToGroup(group_id, provider.get());
   providers_.push_back(provider.release());  // Takes ownership.
 }
 
 void SearchController::OnResultsChanged() {
   if (dispatching_query_)
     return;
 
   KnownResults known_results;
   if (history_ && history_->IsReady()) {
     history_->GetKnownResults(base::UTF16ToUTF8(search_box_->text()))
         ->swap(known_results);
   }
 
   mixer_->MixAndPublish(is_voice_query_, known_results);
 }
 
 }  // namespace app_list