IDL compiler: add array tests

Test-only change.
(Readonly) arrays attributes are already supported by IDL compiler;
this adds tests for them (and makes a few other test fixes).

BUG=239771

Review URL: https://codereview.chromium.org/25474003

git-svn-id: svn://svn.chromium.org/blink/trunk@158687 bbb929c8-8fbe-4397-9dbb-9b2b20218538