Deflake close-on-unload layout tests

Tests using close-on-unload_wsh.py could interfere with each other when
run simultaneously, leading to flakiness.

Fixed by including the name of the test in a query parameter.

Tests can still interfere with themselves, eg.

run_webkit_tests.sh -f --iterations=10 \
    http/tests/websocket/close-on-unload.html

will show some failures, but this is probably harmless and not worth
fixing.

BUG=343452
TEST=run_webkit_tests.sh -f http/tests/websocket

Review URL: https://codereview.chromium.org/171533009

git-svn-id: svn://svn.chromium.org/blink/trunk@167513 bbb929c8-8fbe-4397-9dbb-9b2b20218538