IDL compiler: fix uncapitalization, add test for attribute configuration

Remaining: 40 => 30

BUG=239771
R=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/147493007

git-svn-id: svn://svn.chromium.org/blink/trunk@166379 bbb929c8-8fbe-4397-9dbb-9b2b20218538