Add flag "distillability-dev" for distillability development

components/dom_distiller/core/dom_distiller_switches.h

Index: components/dom_distiller/core/dom_distiller_switches.h
diff --git a/components/dom_distiller/core/dom_distiller_switches.h b/components/dom_distiller/core/dom_distiller_switches.h
index 6b89533c342153af3b971004d44af88c3bf6b05f..482c660705ee8659dee50f536c3fc1b60f4c3849 100644
--- a/components/dom_distiller/core/dom_distiller_switches.h
+++ b/components/dom_distiller/core/dom_distiller_switches.h
@@ -13,6 +13,9 @@ namespace switches {
 // Switch to enable the DOM distiller.
 extern const char kEnableDomDistiller[];
 
+// Switch to enable the distillability dev mode.
+extern const char kDistillabilityDev[];
+
 // Switch to enable synced articles.
 extern const char kEnableSyncArticles[];