Assert we do not leak requests for the system and safe browsing contexts.

chrome/browser/safe_browsing/safe_browsing_service.cc

Index: chrome/browser/safe_browsing/safe_browsing_service.cc
diff --git a/chrome/browser/safe_browsing/safe_browsing_service.cc b/chrome/browser/safe_browsing/safe_browsing_service.cc
index 8ab946eb13da454dcd6703eb65161e32cb95dbaa..a14c250bf49d0e3fec0b74c359619c12c705d129 100644
--- a/chrome/browser/safe_browsing/safe_browsing_service.cc
+++ b/chrome/browser/safe_browsing/safe_browsing_service.cc
@@ -643,6 +643,8 @@ void SafeBrowsingService::InitURLRequestContextOnIOThread(
 void SafeBrowsingService::DestroyURLRequestContextOnIOThread() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
+  url_request_context_->AssertNoURLRequests();
+
   // Need to do the CheckForLeaks on IOThread instead of in ShutDown where
   // url_request_context_getter_ is cleared,  since the URLRequestContextGetter
   // will PostTask to IOTread to delete itself.