Add a skeleton Start Page to the experimental app list.

ui/app_list/app_list_switches.h

Index: ui/app_list/app_list_switches.h
diff --git a/ui/app_list/app_list_switches.h b/ui/app_list/app_list_switches.h
index 853a32f5e3b67260180bafee56825e92e61dea9c..41c42d1824dae0d40664c78500a3e3f7ed6c8f8a 100644
--- a/ui/app_list/app_list_switches.h
+++ b/ui/app_list/app_list_switches.h
@@ -10,11 +10,13 @@
 namespace app_list {
 namespace switches {
 
-APP_LIST_EXPORT extern const char kEnableExperimentalAppList[];
+// Please keep this list sorted.
 APP_LIST_EXPORT extern const char kDisableFolderUI[];
 APP_LIST_EXPORT extern const char kDisableVoiceSearch[];
-APP_LIST_EXPORT extern const char kEnableHotwordAlwaysOn[];
 APP_LIST_EXPORT extern const char kEnableAppInfo[];
+APP_LIST_EXPORT extern const char kEnableExperimentalAppList[];
+APP_LIST_EXPORT extern const char kEnableHotwordAlwaysOn[];
+APP_LIST_EXPORT extern const char kShowAppListStartPage[];
 
 bool APP_LIST_EXPORT IsFolderUIEnabled();
 
@@ -26,6 +28,8 @@ bool APP_LIST_EXPORT IsAppInfoEnabled();
 
 bool APP_LIST_EXPORT IsExperimentalAppListEnabled();
 
+bool APP_LIST_EXPORT IsStartPageWebUIEnabled();
+
 }  // namespace switches
 }  // namespace app_list