Remove TODO for mime-sniffing of mpeg types.

Remove TODO for mime-sniffing of mpeg types.

The following TODO existed in mime_sniffer.cc since 2008:

// TODO(abarth): we don't handle partial byte matches yet
// MAGIC_NUMBER("video/mpeg", "\x00\x00\x01\xB")
// MAGIC_NUMBER("audio/mpeg", "\xFF\xE")
// MAGIC_NUMBER("audio/mpeg", "\xFF\xF")

video/mpeg is not sniffed by Firefox or IE, and is not required to be sniffed by the spec at https://mimesniff.spec.whatwg.org/.

audio/mpeg is already sniffed for the common case where the file starts with an ID3 tag. The uncommon case where it starts with "\xFF\xF." is too broad (it matches the little-endian UTF-16 byte-order-mark), and is not required by the spec.

Remove the TODO.

TEST=net_unittests
BUG=

Committed: https://crrev.com/84dd027af9afa68a49768dfa10fca51610575ae3
Cr-Commit-Position: refs/heads/master@{#329317}

[Adam Rice, 2015-05-08 16:41:34]

ricea@chromium.org changed reviewers:
+ rsleevi@chromium.org

[Adam Rice, 2015-05-08 16:41:34]

Alternatively I could just remove the TODO comment.

[Adam Rice, 2015-05-08 17:30:01]

The pattern for audio/mpeg matches the UTF-16LE byte-order-mark. I don't know if
it can be made more specific, or if we should just go with plan B and delete the
TODO.

[Ryan Sleevi, 2015-05-08 19:30:42]

Can you please revert the whole-file formating? git cl format should only format
the changed lines. Alternatively, upload your patchset w/o any of the formatting
(bypassing presubmit if needed), and then we'll format after the review.

I'm especially NOT keen to introduce new mime sniffing. Just because there is a
TODO does *NOT* make it correct. Unless there is strong justification for it
(and it seems like it's just a TODO), and an interoperable one, then I'm afraid
I'll have to Not LGTM the change.

[Adam Rice, 2015-05-11 10:59:44]

After some additional research, I've changed the CL to just remove the
TODO. Firefox and IE do not sniff video/mpeg, and the standard does not
require it. Except when it starts with an ID3 tag (which is already
supported), audio/mpeg is too ambiguous to sniff simply. The standard
has a TODO for the non-ID3 case.

[Ryan Sleevi, 2015-05-12 01:12:06]

The CQ bit was checked by rsleevi@chromium.org

[Ryan Sleevi, 2015-05-12 01:12:07]

lgtm

[commit-bot: I haz the power, 2015-05-12 01:13:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1138483004/20001

[commit-bot: I haz the power, 2015-05-12 02:11:38]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-12 02:12:59]

Patchset 2 (id:??) landed as
https://crrev.com/84dd027af9afa68a49768dfa10fca51610575ae3
Cr-Commit-Position: refs/heads/master@{#329317}