Fix a crash due to UserScriptListener unregistering notifications on the wrong

chrome/browser/renderer_host/resource_dispatcher_host.cc

Index: chrome/browser/renderer_host/resource_dispatcher_host.cc
diff --git a/chrome/browser/renderer_host/resource_dispatcher_host.cc b/chrome/browser/renderer_host/resource_dispatcher_host.cc
index 8837247fc6e1f44b3573834ee1591117aa41df5c..4c3c8b2fb4e4b4a29e49b42e88a497c5d60e94d4 100644
--- a/chrome/browser/renderer_host/resource_dispatcher_host.cc
+++ b/chrome/browser/renderer_host/resource_dispatcher_host.cc
@@ -194,6 +194,8 @@ ResourceDispatcherHost::~ResourceDispatcherHost() {
   AsyncResourceHandler::GlobalCleanup();
   STLDeleteValues(&pending_requests_);
 
+  user_script_listener_->ShutdownMainThread();
+
   // Clear blocked requests if any left.
   // Note that we have to do this in 2 passes as we cannot call
   // CancelBlockedRequestsForRoute while iterating over