DEPS.xwalk: Roll chromium-crosswalk (634d34e4 -> 15a25d19).

15a25d1 Merge pull request #145 from wang16/resource_m35
4423c80 [Android] Address Context leak in ResourceExtractor
6f158d0 [Android] Revert "Make the ResourceExtractor use the App context"
0eae511 Merge pull request #143 from halton/nacl
0151e36 [Backport] Add base.gyp:base_static as dependency of nacl component
Merge pull request #1821 from wang16/roll_deps

DEPS.xwalk: Roll chromium-crosswalk (634d34e4 -> 15a25d19).