zlib.h, as a result of the Chromium patch 0001-simd.patch, renames read_buf to Cr_z_read_buf with a macro in names.h. Since read_buf is a common function name in other parts of the code, this will affect those other parts randomly, depending on if zlib.h was included before read_buf was mentioned.
In jumbo build experiments the result was link problems because some //net .h files were included after zlib.h, resulting in references to functions named Cr_z_read_buf(...), while zlib.h wasn't included in the .cc file so the object file contained read_buf(...)
I talked with davidben about this and he recommended changing zlib to not touch read_buf. Since the exposure of read_buf is of our own doing, it's a natural change which doesn't require any new patches.
Comment 1 by bugdroid1@chromium.org
, Jan 11 2018