Handle tries of results data in upload (fix _is_directory) for TestResultsServer

The file handler was getting confused when we would upload a full_results.json
that contained a "results" key that pointed to a trie of tests.

Also fix some file permissions issues that the presubmit check complained about.

R=ojan@chromium.org
BUG=403663
NOTRY=true

Review URL: https://codereview.chromium.org/475503005

git-svn-id: svn://svn.chromium.org/blink/trunk@180310 bbb929c8-8fbe-4397-9dbb-9b2b20218538