Mojo: Log an error when we fail to find a JS module.

BUG=328119

Review URL: https://codereview.chromium.org/401723002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285023 0039d316-1c4b-4281-b951-d872f2087c98

gin/modules/file_module_provider.cc

@@ -40,6 +40,7 @@ void AttempToLoadModule(const base::WeakPtr<Runner>& runner,
     runner->Run(source, id);
     return;
   }
+  LOG(ERROR) << "Failed to load module from disk: " << id;
 }
 
 }  // namespace