Fix font issue for some sites using offline reading mode.

Custom fonts (e.g. WebFonts) were not properly serialized and
resulted in unexpected behavior when a picture was saved for
offline reading. This CL serializes the custom font so that we
can use it later when playing the picture back.

bug: 5388379
Change-Id: Ic29e9bf10ac70c46a45f3902ea93558b235fd2dd
1 file changed