fix virtual_test_suites() for browser_test ports

Fix virtual_test_suites() for browser_test ports

In r181420 we started pulling the list of virtual test suites to run
from LayoutTests/VirtualTestSuites (a new file). The browser_test ports
do not pull their tests from that directory, and need a different list
of suites, but I forgot to override the port.virtual_test_suites() call
in their implementations.

The browser_test ports don't currently need or have any virtual test suites,
so this patch implements returning an empty list and adds tests to ensure
that we would catch this regression if it happened again.

We also rework the browser_test_unittest.py tests to eliminate a bunch of duplication and make it clearer that the tests are shared and testing the same behavior.

TBR=thestig@chromium.org
BUG=413986
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=181962

[Dirk Pranke, 2014-09-13 17:12:06]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2014-09-13 17:12:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/569913002/1

[commit-bot: I haz the power, 2014-09-13 17:29:08]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-13 17:29:09]

Try jobs failed on following builders:
  linux_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/2...)

[Lei Zhang, 2014-09-13 17:31:13]

lgtm

https://codereview.chromium.org/569913002/diff/1/Tools/Scripts/webkitpy/layou...
File Tools/Scripts/webkitpy/layout_tests/port/win_unittest.py (right):

https://codereview.chromium.org/569913002/diff/1/Tools/Scripts/webkitpy/layou...
Tools/Scripts/webkitpy/layout_tests/port/win_unittest.py:33: from
webkitpy.common.system.systemhost import SystemHost
nit: alphabetical order?

[Dirk Pranke, 2014-09-13 22:45:56]

https://codereview.chromium.org/569913002/diff/1/Tools/Scripts/webkitpy/layou...
File Tools/Scripts/webkitpy/layout_tests/port/win_unittest.py (right):

https://codereview.chromium.org/569913002/diff/1/Tools/Scripts/webkitpy/layou...
Tools/Scripts/webkitpy/layout_tests/port/win_unittest.py:33: from
webkitpy.common.system.systemhost import SystemHost
whoops. Yeah :).

[Dirk Pranke, 2014-09-14 22:33:20]

Patchset #2 (id:20001) has been deleted

[Dirk Pranke, 2014-09-14 22:33:39]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2014-09-14 22:34:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/569913002/40001

[commit-bot: I haz the power, 2014-09-14 23:59:09]

Committed patchset #2 (id:40001) as 181962