[net] Remove logic for fixing up Gzip encoding type for downloads.

Some servers incorrectly send 'Content-Encoding: gzip' for responses
that should be downloaded as gzipped files. UMA indicates that the
number of servers that exhibit this incorrect behavior is vanishingly
small. Hence the network stack  will no longer perform this encoding
fixup.

What an embedder of the network stack does with a response often depends
on the response headers and the capabilities of the embedder. The
current implementation was based on an inaccurate prediction of the
inteded disposition of the response. In addition to the inaccuracy, the
implementation was also becoming a maintenance burden.

With this change, resources downloaded with the incorrect
Content-Encoding will be saved uncompressed.

BUG=318217

Review URL: https://codereview.chromium.org/1008873006

Cr-Commit-Position: refs/heads/master@{#321890}
11 files changed