Add a temporary check to investigate NavigationThrottle crash

content/browser/frame_host/navigation_handle_impl.h

Index: content/browser/frame_host/navigation_handle_impl.h
diff --git a/content/browser/frame_host/navigation_handle_impl.h b/content/browser/frame_host/navigation_handle_impl.h
index 05fd51b502b0175f2e538a56558368fb5268b4e6..209f2115bf490f24aa4533c78ccf5f9854790c8a 100644
--- a/content/browser/frame_host/navigation_handle_impl.h
+++ b/content/browser/frame_host/navigation_handle_impl.h
@@ -591,6 +591,10 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
   // crbug.com/704892.
   bool is_in_constructor;
 
+  // TODO(clamy): Remove this when we understand the root cause behind
+  // crbug.com/736658.
+  bool throttles_have_been_added_ = false;
+
   base::WeakPtrFactory<NavigationHandleImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(NavigationHandleImpl);