Adds support for navigating to a fragment on the currenty visible document
without waiting for a DOM event that the document has been fully loaded.
This addresses https://github.com/mozilla/geckodriver/issues/150.
MozReview-Commit-ID: 7uiPT5cjGQE
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extra : rebase_source : f9152a6623a25c17e10dc3bc6552b8e635c21317
Andreas Tolfsen