DEPS.xwalk: Roll chromium-crosswalk (6488cb7->f8b103e)

f8b103e Merge pull request #172 from xingnan/1833
dcf89f9 [Android] Fix the crash of GetUserMedia
Merge pull request #2123 from xingnan/1833

DEPS.xwalk: Roll chromium-crosswalk (6488cb7->f8b103e)