Add comment about SK_WHITELIST_SERIALIZED_TYPEFACES flag in build_chromium
Add comment about SK_WHITELIST_SERIALIZED_TYPEFACES flag in build_chromium

BUG=skia:5360

Review-Url: https://codereview.chromium.org/2046543002

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot