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

ui/app_list/search_controller.h

Index: ui/app_list/search_controller.h
diff --git a/ui/app_list/search_controller.h b/ui/app_list/search_controller.h
index 24825339a0c347ca133601731d6248221605d303..ded88507d0f6fd6abfd4bcb8340cdb59e70594d0 100644
--- a/ui/app_list/search_controller.h
+++ b/ui/app_list/search_controller.h
@@ -39,9 +39,11 @@ class APP_LIST_EXPORT SearchController {
                           int action_index,
                           int event_flags);
 
+  // Adds a new mixer group. See Mixer::AddGroup.
+  size_t AddGroup(size_t max_results, double boost);
+
   // Takes ownership of |provider| and associates it with given mixer group.
-  void AddProvider(Mixer::GroupId group,
-                   scoped_ptr<SearchProvider> provider);
+  void AddProvider(size_t group_id, scoped_ptr<SearchProvider> provider);
 
  private:
   typedef ScopedVector<SearchProvider> Providers;