DevTools: add ParseAuthorStyleSheet events to Timeline

The operation may take noticable time an may give the user additional information about his page performance.

BUG=424502

Review URL: https://codereview.chromium.org/717573003

git-svn-id: svn://svn.chromium.org/blink/trunk@185190 bbb929c8-8fbe-4397-9dbb-9b2b20218538