Add a skeleton Start Page to the experimental app list.

ui/app_list/app_list_switches.cc

Index: ui/app_list/app_list_switches.cc
diff --git a/ui/app_list/app_list_switches.cc b/ui/app_list/app_list_switches.cc
index 57c31ed41d5352aed588207207bbf956be7a737f..4bb47cf8c4fa5f63495198d36ef6bc75f006f77e 100644
--- a/ui/app_list/app_list_switches.cc
+++ b/ui/app_list/app_list_switches.cc
@@ -21,6 +21,9 @@ const char kDisableVoiceSearch[] = "disable-app-list-voice-search";
 // If set, the app info context menu item is available in the app list UI.
 const char kEnableAppInfo[] = "enable-app-list-app-info";
 
+// If set, the app list will show the start page webui.
+const char kShowAppListStartPage[] = "show-app-list-start-page";
+
 bool IsFolderUIEnabled() {
   return CommandLine::ForCurrentProcess()->HasSwitch(kEnableFolderUI);
 }
@@ -43,5 +46,9 @@ bool IsExperimentalAppListEnabled() {
       kEnableExperimentalAppList);
 }
 
+bool IsStartPageWebUIEnabled() {
+  return CommandLine::ForCurrentProcess()->HasSwitch(kShowAppListStartPage);
+}
+
 }  // namespace switches
 }  // namespace app_list