Given:
a.href = "over 9000!"
Then:
a.href === BASE_URL + '/over%209000!';
This commits adds an escape: bool option to URL.resolve which will escape the
path, query and fragment when true.
Also changes the Anchor, Image, Link and IFrame getSrc to escape. Escaping is
also used when navigating a frame.
We often verify the correctness of tests by loading them in an external browser,
but some tests just don't run the same/correctly. For example, we used to hard-
code the http://127.0.0.1:9582/ origin, but that would cause tests to fail if
running from a different origin.
This commit _begins_ the work of improving this. It introduces a
testing.ORIGIN, testing.BASE_URL and testing.HOST which will work correctly in
both our runner and an external browser.
It also introduces `testing.IS_TEST_RUNNER` boolean flag so that tests which
have no chance of working in an external browser (e.g. screen.width) can be
skipped.
The goal is to reduce/remove tests which fail in external browsers so that such
failures aren't quickly written off as "just how it is".
