[abort] [webkit test runner] Complete location change when a frame is detached.

[webkit test runner] Complete location change when a frame is detached.

When working on http://crrev.com/181493007 I found that the
fast/loader/unload-hyperlink-targeted.html
LayoutTest would hang with that change.
It seems to be a mix of two issues:
 1) during the execution of this tests the child frame becomes the
 topLoadingFrame (this is the case with and without the linked patch),
 and so the test runner waits for it to finish,
 2) the child frame is gets detached after the load has
 committed but before it had finished. This still results in the top frame
 reporting the load had finished but the child frame only ends up calling
 didAbortLoad and frameDetached.
The combination of these issues leads to the test runner waiting for the
detached frame to finishLoading (which it never does leading to a hang).
The fix is to complete the ongoing navigation when the frame is detached.

BUG=325351
TESTS=run_webkit_tests.py