DevTools: [JsDocValidator] Fix interface detection for plain named functions

The validator used to fail to detect interfaces written as "function Ifc() {..}"

R=sergeyv@chromium.org, sergeyv, yurys

Review URL: https://codereview.chromium.org/376553005

git-svn-id: svn://svn.chromium.org/blink/trunk@177662 bbb929c8-8fbe-4397-9dbb-9b2b20218538