[Android] Fix the build from scratch after 60636ca.

ninja: error: 'xwalk_xwview_test/assets/broadcast.html', needed by 'xwalk_core_internal_test_apk/codegen.stamp', missing and no known rule to make it
Merge pull request #2188 from rakuco/fix-for-60636ca

[Android] Fix the build from scratch after 60636ca.