Revert of Add a temporary check to investigate NavigationThrottle crash

content/browser/frame_host/navigation_handle_impl.cc

Index: content/browser/frame_host/navigation_handle_impl.cc
diff --git a/content/browser/frame_host/navigation_handle_impl.cc b/content/browser/frame_host/navigation_handle_impl.cc
index 388143d8c9dcccd32a880bde90fba7bc11dd2eef..9e6c1fc1bd3e8a03ad3babb122673881e34a2ad4 100644
--- a/content/browser/frame_host/navigation_handle_impl.cc
+++ b/content/browser/frame_host/navigation_handle_impl.cc
@@ -1091,11 +1091,6 @@
 }
 
 void NavigationHandleImpl::RegisterNavigationThrottles() {
-  // TODO(clamy): Remove this when we understand the root cause behind
-  // crbug.com/736658.
-  CHECK(!throttles_have_been_added_);
-  throttles_have_been_added_ = true;
-
   // Register the navigation throttles. The vector returned by
   // CreateThrottlesForNavigation is not assigned to throttles_ directly because
   // it would overwrite any throttles previously added with