Fix issue with too much padding on base64 data.
Fix issue with too much padding on base64 data.

TBR=mtklein
BUG=skia:

Review URL: https://codereview.chromium.org/663573004

Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot