DEPS.xwalk: Roll chromium-crosswalk (66c669a -> c8d2f7c)

c8d2f7c Merge pull request #195 from rakuco/ignore-khronos-CL
22479b2 .gitignore: Ignore src/third_party/khronos/CL.
Merge pull request #2483 from rakuco/roll-cr-crosswalk-CL-ignore

DEPS.xwalk: Roll chromium-crosswalk (66c669a -> c8d2f7c)