javascript: urls should always be parsed synchronously

Removing the minimumLayoutDelay() threshold as part of:
https://codereview.chromium.org/20140002/

revealed that we weren't always parsing javascript: urls
synchronously.  This change is a preventative fix to allow
me to move forward with this change.

In order to trigger this in current webkit, we'd need to parse
a javascript: url which included a script which took more than .5
seconds to execute and then had a second script tag.
We'd (incorrectly) yield between the two script tags while parsing
the html result of the javascript: url.

I also renamed the isLayoutTimer active method on Document to
better reflect what it's actually used for.

I also added a FIXME to WebViewImpl.

BUG=264489
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/20553003

git-svn-id: svn://svn.chromium.org/blink/trunk@154949 bbb929c8-8fbe-4397-9dbb-9b2b20218538