Quick CL, just handling some exceptional cases.
Also renames 'should_keep_attribute_alive' to 'is_keep_alive_for_gc':
more explicit (GC), removes the redundant 'attribute', and the vague 'should' ('is' clearly means boolean).

(Also Jinja whitespace/formatting fixes.)

BUG=239771

Review URL: https://chromiumcodereview.appspot.com/24708002

git-svn-id: svn://svn.chromium.org/blink/trunk@158393 bbb929c8-8fbe-4397-9dbb-9b2b20218538