video_VideoSeek: pass immediately for vp8 switchres nyan

After discussion, we return run_once immediately to make the test
skipped (and passed) instead of raising TestNAError.

BUG=chromium:723982
TEST=manual test

Change-Id: I3851bc549af692583437bc2f5d69304d774ffa52
Reviewed-on: https://chromium-review.googlesource.com/522305
Commit-Ready: Pin-chih Lin <johnylin@chromium.org>
Tested-by: Pin-chih Lin <johnylin@chromium.org>
Reviewed-by: Kuang-che Wu <kcwu@chromium.org>
diff --git a/client/site_tests/video_VideoSeek/video_VideoSeek.py b/client/site_tests/video_VideoSeek/video_VideoSeek.py
index 1470304..5e6cf94 100755
--- a/client/site_tests/video_VideoSeek/video_VideoSeek.py
+++ b/client/site_tests/video_VideoSeek/video_VideoSeek.py
@@ -53,7 +53,8 @@
         @param video: Sample video file to be seeked in Chrome.
         """
         if self.is_skipping_test(codec, is_switchres):
-            raise error.TestNAError('Skipping test run on this board.')
+            logging.info('Skipping test run on this board.')
+            return  # return immediately to pass this test
 
         with chrome.Chrome(
                 extra_browser_args=helper_logger.chrome_vmodule_flag(),