[zoom bubble] First part of speculative fix for zoom bubble crashes.

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 6b0de350b29e627cbc81545a3cd5e2cd61ecdbe6..d0363a7ae76a9d5fc1486e19e04a1823eeb947ca 100644
--- a/chrome/browser/ui/zoom/zoom_controller.cc
+++ b/chrome/browser/ui/zoom/zoom_controller.cc
@@ -79,6 +79,8 @@ void ZoomController::UpdateState(const std::string& host) {
   if (host.empty())
     return;
 
+  CHECK(web_contents());  // http://crbug.com/144879
+
   // Use the active navigation entry's URL instead of the WebContents' so
   // virtual URLs work (e.g. chrome://settings). http://crbug.com/153950
   content::NavigationEntry* active_entry =