Mark test-rightsizing-b.xhtml flaky
Mark test-rightsizing-b.xhtml flaky

It seems test-rightsizing-b.xhtml failed on Linux platform.
Other platforms are fine with this test.

BUG=495523
NOTRY=true
TBR=fmalita@chromium.org

Review URL: https://codereview.chromium.org/1233233004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@198905 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk