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

chrome/browser/ui/app_list/search/search_controller_factory.cc

Index: chrome/browser/ui/app_list/search/search_controller_factory.cc
diff --git a/chrome/browser/ui/app_list/search/search_controller_factory.cc b/chrome/browser/ui/app_list/search/search_controller_factory.cc
index d1a5a2c4caab4d04b2a1d8ea4f4fc6163c0eba60..6bdfdd8bb57e4845fcbd45eeef42c55bf548abf1 100644
--- a/chrome/browser/ui/app_list/search/search_controller_factory.cc
+++ b/chrome/browser/ui/app_list/search/search_controller_factory.cc
@@ -23,6 +23,13 @@ namespace app_list {
 
 namespace {
 
+// Maximum number of results to show in each mixer group.
+const size_t kMaxAppsGroupResults = 4;
+const size_t kMaxOmniboxResults = 0;  // Unlimited.
+const size_t kMaxWebstoreResults = 2;
+const size_t kMaxPeopleResults = 2;
+const size_t kMaxSuggestionsResults = 6;
+
 // Constants related to the SuggestionsService in AppList field trial.
 const char kSuggestionsProviderFieldTrialName[] = "SuggestionsAppListProvider";
 const char kSuggestionsProviderFieldTrialEnabledPrefix[] = "Enabled";
@@ -45,22 +52,37 @@ scoped_ptr<SearchController> CreateSearchController(
   scoped_ptr<SearchController> controller(new SearchController(
       search_box, results, HistoryFactory::GetForBrowserContext(profile)));
 
-  controller->AddProvider(Mixer::MAIN_GROUP,
+  // Add mixer groups. There are four main groups: apps, people, webstore and
+  // omnibox. The apps, people and webstore groups each have a fixed maximum
+  // number of results. The omnibox group fills the remaining slots (with a
+  // minimum of one result).
+  size_t apps_group_id = controller->AddGroup(kMaxAppsGroupResults, 3.0);
+  size_t omnibox_group_id = controller->AddGroup(kMaxOmniboxResults, 2.0);
+  size_t webstore_group_id = controller->AddGroup(kMaxWebstoreResults, 1.0);
+  size_t people_group_id = controller->AddGroup(kMaxPeopleResults, 0.0);
+  // The omnibox group is treated specially by the Mixer and must have the
+  // correct ID.
+  DCHECK_EQ(omnibox_group_id, Mixer::OMNIBOX_GROUP);
+
+  // Add search providers.
+  controller->AddProvider(apps_group_id,
                           scoped_ptr<SearchProvider>(new AppSearchProvider(
                               profile, list_controller,
                               make_scoped_ptr(new base::DefaultClock()))));
-  controller->AddProvider(Mixer::OMNIBOX_GROUP,
+  controller->AddProvider(omnibox_group_id,
                           scoped_ptr<SearchProvider>(
                               new OmniboxProvider(profile, list_controller)));
-  controller->AddProvider(Mixer::WEBSTORE_GROUP,
+  controller->AddProvider(webstore_group_id,
                           scoped_ptr<SearchProvider>(
                               new WebstoreProvider(profile, list_controller)));
   controller->AddProvider(
-      Mixer::PEOPLE_GROUP,
+      people_group_id,
       scoped_ptr<SearchProvider>(new PeopleProvider(profile, list_controller)));
   if (IsSuggestionsSearchProviderEnabled()) {
+    size_t suggestions_group_id =
+        controller->AddGroup(kMaxSuggestionsResults, 3.0);
     controller->AddProvider(
-        Mixer::SUGGESTIONS_GROUP,
+        suggestions_group_id,
         scoped_ptr<SearchProvider>(
             new SuggestionsSearchProvider(profile, list_controller)));
   }