You may think that https://codereview.chromium.org/8806004 , back in
2011, did this. However, that's not correct. That update only patched files which
were present in both our old, customized checkout and zlib 1.2.5.

In zlib 1.2.5, gzio.c was replaced with gzclose.c, gzguts.h, gzlib.c, gzread.c
and gzwrite.c. We did not add those files. We just used the gzio.c from 1.2.3
with our custom patches from Gears, together with the rest of 1.2.5.

This unholy chimera worked until I went ahead and tried to fix the broken
mangling for 64 bit API symbols. See
https://codereview.chromium.org/13473020/ . This uncovered the lack of
gzread64, which was, after that fix, referenced by libxml. Since gzio.c from
1.2.3 doesn't have gzread64, this was something of a problem. I'm thus
finishing the update.

R=agl@chromium.org,rsleevi@chromium.org,brettw@chromium.org,bradchen@chromium.org
BUG=None

Review URL: https://chromiumcodereview.appspot.com/13564004

Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 17f706d599cfb296c633a12bc32f7bbf5633e6d9