Extended timeout for screenshot sync test

R=ccameron@chromium.org
TBR=kbr@chromium.org
BUG=256848

Review URL: https://codereview.chromium.org/131293007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248310 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248310