Add tests for the BrowserActionsContainer in overflow mode

chrome/browser/extensions/extension_toolbar_model.h

Index: chrome/browser/extensions/extension_toolbar_model.h
diff --git a/chrome/browser/extensions/extension_toolbar_model.h b/chrome/browser/extensions/extension_toolbar_model.h
index 05b143d89985dada27060394a545658677fd5364..bf42f7ce332a3f66eed7f6d25321d17d0e1f0c52 100644
--- a/chrome/browser/extensions/extension_toolbar_model.h
+++ b/chrome/browser/extensions/extension_toolbar_model.h
@@ -144,6 +144,9 @@ class ExtensionToolbarModel : public content::NotificationObserver,
   // number of visible icons will be reset to what it was before highlighting.
   void StopHighlighting();
 
+  // Sets the number of visible icons and notifies all observers of the change.
+  void SetVisibleIconCountForTest(size_t visible_icons);
+
  private:
   // content::NotificationObserver:
   virtual void Observe(int type,