Add non-wrapped types to IDL compiler

Small CL, adding some more type handling and implementing general case of should_keep_attribute_alive.
(Minor refactoring as well.)

4 new types supported (for readonly attributes):
DOMString, DOMTimeStamp, SerializedScriptValue, any

BUG=239771

Review URL: https://chromiumcodereview.appspot.com/24421002

git-svn-id: svn://svn.chromium.org/blink/trunk@158349 bbb929c8-8fbe-4397-9dbb-9b2b20218538