Add support for ByteString and USVString to IdlArray#assert_type_is.
Add support for ByteString and USVString to IdlArray#assert_type_is.

zqzhang/testharness.js,ayg/testharness.js,bboyle/testharness.js,hallvors/testharness.js,RatneshThakur/testharness.js,hallvors/testharness.js,jyasskin/testharness.js,jyasskin/testharness.js