[zoom bubble] Add tests for ZoomController::UpdateState() handling empty hosts.

chrome/browser/ui/zoom/zoom_controller.cc

Index: chrome/browser/ui/zoom/zoom_controller.cc
diff --git a/chrome/browser/ui/zoom/zoom_controller.cc b/chrome/browser/ui/zoom/zoom_controller.cc
index d8ae5a8398212ae2fb92a2a6f16e310c28d3a758..f862b2969f6ac5bf48a3f1f8a69defd37fb1559c 100644
--- a/chrome/browser/ui/zoom/zoom_controller.cc
+++ b/chrome/browser/ui/zoom/zoom_controller.cc
@@ -40,10 +40,7 @@ ZoomController::ZoomController(content::WebContents* web_contents)
   UpdateState(std::string());
 }
 
-ZoomController::~ZoomController() {
-  default_zoom_level_.Destroy();
-  registrar_.RemoveAll();
-}
+ZoomController::~ZoomController() {}
 
 bool ZoomController::IsAtDefaultZoom() const {
   return content::ZoomValuesEqual(web_contents()->GetZoomLevel(),