resourceloader: Never defer execution for top loading modules

resourceloader: Never defer execution for top loading modules

There was a bug where if a module was in the top queue but had CSS,
its execution would be deferred until its CSS was ready. This would
cause the module's execution to occur after document ready and after
user scripts had run.

This is bad because top-loaded modules are supposed to be guaranteed
to run before document ready.

Fix this by skipping the wait-for-CSS logic when loading synchronously.
Top-loading modules' execution is now guaranteed to block loading the
rest of the page, but their CSS isn't guaranteed to be ready at this
point. Which is fine, because they shouldn't be measuring things in the
DOM before document ready anyway.

Change-Id: I5779cdef336be184741ad97ea84113eb7790dd39