DEPS.xwalk: Roll blink-crosswalk bc7b6c1 -> b8fedaf

b8fedaf Merge pull request #24 from pozdnyakov/fix_the_viewport
3a072fd Fix the --enable-viewport command line option
Merge pull request #2480 from pozdnyakov/roll_blink_xwalk

DEPS.xwalk: Roll blink-crosswalk bc7b6c1 -> b8fedaf